Ongoing Sentinel Prime Analysis

Introduction
This essay is designed to give the readers, and indeed fandom, a more accurate portrait of Sentinel Prime. Fanon (that is, beliefs held by a significant portion of a fanbase) holds Sentinel's character to be the kind of person who eats kittens for breakfast and flavors his coffee with the tears of small children. Such is not the case, illustrated in the following facts and evidence and a little critical thinking.

Season One
Transform and Roll Out! parts I-III

Along Came a Spider
FLASHBACK I
Sentinel's initial transformation ends with a classic "strong man" pose. This is appropriate, as Sentinel's character design implies physical strength and it helps to illustrate the youthful spirit Sentinel was at one time.
Sentinel teases Optimus in this flashback, as friends often do. If teasing automatically equates jerkery, God, I'm so mean to tazunajo.
Here's one of my favorite moments—Sentinel and Elita walking together. Sentinel keeps an arm around her shoulder—and it actually, in fact, does end up around her waist by the time they ground gives way beneath them.

FLASHBACK II
"Energon-y goodness." Okay: Yes, this is a mild reference to the Tick. Yes, Sentinel was voiced by Townsend Coleman, is blue and has a larger than average chin, just like the Tick. That was a joke the writers threw in there. It was funny once. Over 9000 times later? Not so much.
Spider slings its webbing at Optimus and Elita. What does Optimus do? He runs, meaning Elita takes the hit. What does Sentinel do response? Runs over to her and cuts her free to make sure she's okay.
Spider attacks Sentinel and Elita. What does Sentinel do? He takes a bite for her.
When Elita chooses to download Sentinel's ability to use the Skyboom shield to kill the spider, she touches Sentinel's hand. Notice in Flashback III that when she downloads Optimus' grapplers, she touches his shoulder—an area less intimate than the hand.
When Elita returns the Skyboom shield to Sentinel, they look at each other a lot longer than Elita ever looked at Optimus.
Sentinel not wanting to leave the planet (canonically named Archa VII in The AllSpark Almanac) shows a lot about him as well—he hates to leave things unfinished, which speaks a lot to his work ethics.
Another one of my favorite moments—Sentinel uses the Skyboom shield to hold back the spiders, calling out to Elita and Optimus, "Go! I'll cover your retreat!" Gee, he's pretty selfless, risking his life and all that.
Also in this moment, when Sentinel is fighting off the spiders, Optimus wastes no time in transforming and running like hell. Elita, on the other hand, hesitates, watching Sentinel for a moment, then runs away.

FLASHBACK III
In Elita's first two lines of dialogue with Optimus, she is extremely short with him, even looking at him like he's a moron at one point (It's useless on organics, remember?).
When Elita falls back into the lower levels of the caves, Optimus makes one effort to save her. When this effort fails, he does nothing else.
Conversely, when Sentinel realizes what's happened, he scream Elita's name and is more than willing to throw himself into the inferno to save her, insisting, "We need to go after her!"
When Optimus tells Sentinel there's "no time" and forces him to leave Elita behind, you can see Sentinel wilting in resignation.
Although Sentinel insists they go back for Elita once he and Optimus are above ground, the expression on his face as he looks at the fire and smoke billowing up from the caves is one of fear and a degree of hopelessness.
When Optimus informs him that Elita is "offline," Sentinel is heartbroken at his loss, and enraged that Optimus insisted they leave Elita behind, which is expressed in Sentinel screaming, "This is all your fault…!"

Season Two
The Elite Guard
Much of the grief Sentinel catches comes from his insistence that there are no Decepticons on the planet, which usually intercuts to a shot of Megatron or another Decepticon. This serves what the fiction and theatre communities refer to as dramatic irony—that is, the audience is savvy to X, but the characters aren't. In this case, the audience is aware that the Decepticons are masking their energy signatures, but the characters aren't. There is also another facet: Anyone who has written a report, be it for school or for work, has had to back up their findings with hard evidence. Such is the case here—the ship's scanners indicated that the planet was clear, which would have stood up under scrutiny far better than someone's word.

Return of the Headmaster

Mission Accomplished
The first real indication that there are Decepticons on Earth is when Starscream crashes thirty yards away from the main cast and the Elita Guard. Sentinel and Optimus are about the same age, as we can gather from them being former Academy mates; if Optimus had never seen battle against a Decepticon, it stands to reason that Sentinel hasn't either.  
The situation: A passenger train carrying civilians has been rigged to blow up at any given second and Starscream has not only crash landed thirty yards away from the main cast, but shot Ultra Magnus at point blank range—taking him out of commission and leaving Sentinel in charge. Jazz asks Sentinel, "What's our next move?" and Sentinel hesitates. Surprisingly common reaction to being put on the spot, both in and out of combat related scenarios? Yes. Excuse to question, belittle or mock Sentinel's leadership skills? Not so much.  

Auto-boot Camp
A great deal of fans would be swift to point out Sentinel's harsh treatment of Bumblebee and Bulkhead throughout the episode. However, consider his first line in the episode—I am Sentinel Minor, your drill instructor. "Drill instructor" is a title that is also in the human military system—a drill instructor (title varies from branch to branch, and from country to country) is an enlisted personnel whose duty is to indoctrinate recruits and prepare them to be soldiers. You will find similar events in any military film, particularly ones that focus on the US Marine Corps (i.e Full Metal Jacket, Jarhead). The goal of a drill instructor is not to mommy his or her recruits, but to train them to be soldiers to the best of his or her ability. Given Sentinel's affinity for rule-following, stemming from "Along Came a Spider," he is in his element here.

Season Three
Where is Thy Sting?
The scene in question is when the Elite Guard and the Earth Autobots (save Bulkhead) are trying to determine who is Bumblebee and who is Wasp. As Sentinel interrogates "Bumblebee," who is sitting on the sofa, note the former's stance: he's kneeling in front of him, separated only by the coffee table. This is psychological: Sentinel has put himself and "Bumblebee" on an equal level, indicating that he can be deemed trustworthy.

Five Servos of Doom
It has been pointed out that Sentinel's own men don't seem to like him. This is contradicted in two words: Jet Twins. Both Jetfire and Jetstorm openly and greatly admire, in fact worship, Sentinel (listening to his stories with rapt attention, etc.).
"You bots make such a cloud of exhaust about having 'fought Decepticons'—well, I'm capturing them!" Over the course of the episode, Sentinel had placed four Decepticons (Sunstorm, Lugnut, Swindle and Blitzwing, the latter two off-camera) in the brig; had he not been double crossed by Lockdown and Ramjet, he would have gone for five plus. In the course of two full seasons, as well as a part of a third, none of Optimus Prime's men had captured and detained a Decepticon agent. Despite having under the table help, Sentinel has, for want of a better term, one-upped the core cast.
Many are swift to note that Lockdown is a Decepticon, making Sentinel's deal with him morally ambiguous at best. What they forget is the brief backstory we know for Lockdown—in "Thrill of the Hunt," when accused of being a Decepticon, Lockdown denies that he's "one of them." In "A Fistful of Energon," he tells Prowl that the Decepticons pay better on bounties than the Elita Guard. The latter quote implies that he's had dealing with the Guard before. This shows that Lockdown is a neutral, offering his services to the highest bidder. Technically, Lockdown is lumped in with the Decepticons for toy purposes; in cartoon canon, he has a rubsign: a blank place indicating a lack of allegiance to any given faction. Bearing this information in mind, Sentinel's deal with Lockdown wasn't as morally ambiguous as it is played up to be.

Decepticon Air
During the battles outside the Steelhaven, Blitzwing has a gun pointed to Sentinel's head and threatens to shoot him if the other Autobots continue to fight. Sentinel's response: Don't surrender! That's a direct order! Sentinel knew there was a good chance that he would be shot, and yet ordered his troops to fight. He didn't care if he died or not—that is courage, best summarized by John Wayne: "Being scared to death, but saddling up anyway."He placed the good of Cybertron and the good of the mission before his personal safety.

This is Why I Hate Machines
Much of the comments for this episode hinge on the commercial Ratchet and Capt. Fanzone saw outside Maccadam's. This commercial, while off-putting, allowed Sentinel to perform one of his duties as Magnus—keeping the populace informed, and offering them a way to protect them and theirs (in this case, by reporting suspicious activity). Would it have been better for him to do nothing and shrug off any deaths that occurred? No—and he knew that; thus, he took action.
It's been implied that Sentinel used the attack on Ultra Magnus as a way to justify  his role as Magnus. Such is not the case—Sentinel is, as been touched on previous and will be addressed in the next section, Ultra Magnus' lieutenant. Regardless of how it happened (physical incapacity, impeachment, stepping out of the office to get an energon from the Cybertroninan Starbucks™), Sentinel is the one who holds down the fort when Ultra Magnus cannot do so.
Complaints have been lodged (by fans; who knows about the citizens…?) about Sentinel "imprisoning" Cybertron, and about the curfew. To "imprison" someone means to physically put them in jail; such was not the case, as Cybertronians were seen freely walking about the streets. What is more likely the case is a restriction of off-planet travel, as well as curfew—both actions countries can and do take in times of war or heightened political tension.
The other half of the commentary stems from Sentinel's interaction with the High Council, and his proposed handling of Omega Supreme. Omega was known to be carrying the top two Decepticons (Megatron and Starscream), and was essentially a sitting duck. One would be a damn fool to pass the opportunity to be rid of the king pin of the Decepticon military by. Furthermore, Sentinel was calling for a coordinated military strike, as opposed to random pot shots.
In response to this, the Council wanted to deliberate—something that could have taken anywhere from an hour to a year, during which time a second Great War could have broken out. Immediate action was called for.
A final, additional, interesting note is thus—in Transformers Animated canon, the role of Magnus is implied to be the same as Prime in Generation One canon. During the debate in the council chambers, the Council, more specifically Alpha Trion, was challenging the rule of the Magnus.

Miscellaneous Notes and Sources
It's after "Along Came a Spider" when we start to see the Sentinel many fans have come to hate—strict and abiding by the rule book. Consider what happened when Sentinel last broke the rules—he lost Elita, whom he loved very much, and he lost a friend in Optimus. After that, when he became sterner, he alienated those around him as well. The only things he had left were rank and power; his actions since then have been to prevent that loss again—in himself and in others.

His strictness comes from his occupation—at one time, a drill sergeant, and then the second in command and eventually ruler of Cybertron. One does not do any of these things by mommying people.

Portions of the fandom are swift to describe Sentinel as being disrespectful; if he has no respect for anyone, then why does he routinely call Ultra Magnus "sir" and salute him—all military respects? This same portion of fans often elevate Optimus over Sentinel by dint of the former being the "better" mech, and feel Sentinel should kowtow to him. Such is not the case—as Optimus pointed out, he and Sentinel "[were] of equal rank."

Others would like to question his intelligence—or go right for the groin and call him an idiot. Take a moment to look at Sentinel's title: Prime, yes, but also Ultra Magnus' lieutenant. Ultra Magnus (a capable leader in his own right) bypassed two fan favorites (Optimus Prime and Jazz, the latter strongly implied to be Sentinel's lieutenant) to choose Sentinel as his lieutenant, the Cybertronian to take his place if he is unable to lead. Given the responsibility of the job, Ultra Magnus surely had great confidence in Sentinel and his abilities to choose him.

A third portion of the fandom would like to see Sentinel removed from his position as lieutenant (and later Magnus), explicitly or implicitly expressing a wish that Optimus replace him. There are two flaws in this scenario.
— The first is that Optimus has no formal military training. As seen in "Endgame," he was expelled from the Autobot Academy and demoted to space bridge repair duty. This would be like slapping a four-star general rank on a ROTC cadet and asking him or her to win the War in Iraq.  
— Second, there is a cultural standard: the Autobots pride themselves on being everything the Decepticons are not. To impeach Sentinel without proper justification would be to lower themselves to the level of their enemies—something they pride themselves on never doing. Also, there's the simple fact that the action is very reminiscent of the behavior of a child: "We don't like you so you can't be in our club."

Regarding Transformers III: Dark of the Moon
I can't say much, not until I actually see DOTM; at the moment I'm working off of other people's reactions. That being said, regarding the inevitable DOTM / TFA Sentinel comparisons:
The sins of the father are not the sins of the son.

It's not fair to look at DOTM Sentinel and say he's better or worse than TFA Sentinel because of what he did / said / whatever in the film. The characters, while they share the same name, are in different continuities and are operating with different motives (I assume), and under different circumstances. One size does not fit all.

Thank you.

Conclusion
Before accusations start flying like so many Boeing 747's, I don't think Sentinel is the be-all-end all, a paragon of anything—or even perfect, for that matter. He's egotistic and treats Optimus and his crew poorly because of his grudge from Archa VII, and an attitude adjustment would more likely than not benefit him. However, these flaws give him room to grow and become a better character, which is the hallmark of a properly thought out character. His flaws make him human, and thus easier for a willing audience to whom they can connect.

Related Reading
foxtragic, whose essay here helped shape this one in turn.
Sounddrive's short story Friendship of the Unexpected, which pulls information from this essay.

Special Thanks to…
tazunajo