Speaking as someone who just finished rewatching the first movie along with ROTF a few hours ago and is continuing with the other movies... I think it's time most of us did give the movies a rewatch if you haven't done so in a while.

The first movie's portrayal of Prime, while still "Murder-Prime" in a few scenes is easily the closest portrayal of the classic Optimus Prime that a lot of people associate with the character. Note that even when Sector Seven ended up capturing Bumblebee, he held back Autobots who clearly disagreed with his decision to not interfere and save him because as he said, it would end up bringing harm to the humans.

Later on with Bonecrusher, he only engages him in the first place because he was bringing harm to humans on the highway. The Decepticon he was dealing with was clearly not somebody who could be reasoned with diplomatically.

Actually, that is something I want to bring up. The Decepticons in the movies *are not* like how they are usually portrayed in almost every other piece of media. These ones will do anything it takes to get what they need and they actually do go through with it, even including bringing harm to humans if it will serve their purpose. They are not the type of enemy that the Autobots can simply chase off to fight another day like they typically have been. Let them go and you're risking untold amount of damage and lives lost. Look no further than when Scavenger tried escaping, visibly running over humans and laying waste to property.

Even when it came to tensions between the Autobots and humans over why they still remained on Earth in ROTF, Optimus was still compliant and understanding of their fears and reasoning, going so far as to accept the possibility of them having to leave Earth if a decision like that was made while still giving them the ultimatum of "What if you're wrong?" which ultimately ended up being true.

Dark of the Moon, his most trusted and close relationship with Sentinel Prime showing a further glimpse into his softer side, possibly even a further look into his character. This may just be me speaking but I think this incarnation of Prime knows he is flawed, is aware of who he is and may honestly even regret his past actions. Sentinel could have easily taken the Matrix back but even if he was planning on backstabbing him to achieve his goal, he still saw something worthy in Optimus to lead the next generation of Autobots even under the pretense of Earth being a new experience and thus, a new relationship between the two of them.

Then comes the betrayal and Optimus is obviously deeply hurt by it all. For lack of better wording on my part, the man who he likely looked up to and may have even been a sort of Father-figure to him has gone against everything that they both shared in experience with. The same man who has then joined forces with the last person you expected them to and is aiding in not only the destruction and death of their own kind, but also the species they have sweat blood and tears for to protect. On an even larger scale than the previous two movies no less. No matter who you are, I don't think you honestly can say if you were in Optimus' shoes, you wouldn't at least feel partially the same.

And even after all of that, after they were explicitly told they they needed to get the hell out of dodge and away from Earth, Optimus still held onto his self-imposed rule of never bringing harm to a human.

It was only once Age of Extinction came around that he actually broke that rule and who could blame him? Honestly, I don't think much can be said that already wasn't stated and observed in the movie to understand why Prime is feeling how he is. DOTM was the planting of the seeds of betrayal and distrust that AoE ultimately expanded upon and gave us an insight into an end result of Optimus that I personally find far more interesting than some other incarnations we've had over the years. Especially RID01 and the Unicron trilogy, who might as well all be the same character (and two of them even are).

It's a side of Optimus that I wish was explored more often, which is why I ultimately wish there was a cartoon connected to the movies that went into further detail and had the opportunity to explore the characters even further. I damn well love Animated but I do have thoughts from time to time of a "What If?" cartoon more closely tied to the Movieverse.

TLDR - Movie Optimus, while not a complete and total cut-and-paste of past incarnations does inherently carry the spirit of his "Ancestors" but also gives us another look into the character that has never been explored before.

 

They haven't treated his character poorly at all. So what if he's the most aggressive Optimus we've gotten, at least he has more personality and isn't the usual father figure, wise leader type we always get. We've gotten an Optimus who would sacrifice his body for humanity, one who understands the sacrifices sustained during war, losing faith in humanity, seeking vengeance on the people who have killed his friends and an Optimus who has been emotionally lost. These are traits that characterize him and allow him to grow. Just because he's thousands of years old old it doesn't mean he still can't grow. People complain about how the characters on these films lack personality and characterization but often ignore what's right in front of them. At least this is what I think.

 

For all we know, the movies may well be the reason he now feels this way, hmmmm......

 

Not sure if it counts but in 2005 he declined to work on Robot Chicken involving a sketch involving Optimus getting prostate cancer.

 

Hmmm... interesting.