Wow i think the movies are pretty great and do a good job of portraying the cartoons.
I think that the biggest fail of the movies is that none of the actions have any weight. Robots are falling apart, things are exploding, people are dying...but do we really care about any of that? Michael bay doesn't know how to make the audience care about what is happening on screen and we are just kinda sitting there and watching the fireworks for 2 and a half hours.
Maybe you don't care but I know people that were sad when Prime died in the 2nd movie. Actually I know a few people that cried during that part (they were females). I remember watching the cartoon when I was younger and loving it but it was really cheesy when I revisit it now. The movies capture some of that. Also the biggest problem with the movies is Transformers is supposed to be about the Autobots vs. Decepticons yet the movie has added the humans into it. In the cartoon the humans weren't much of a factor at all.
I am still puzzled to see why most people would care about optimus getting killed in the way michael bay decided to present it but sure, lets say that is the case...1 scene where people cared about on screen actions. In a series which is 7.5 hours long.
Also, compare that scene to the way optimus died in the 1985s Transofrmers "the movie" cartoon, and there is no contest. That is an awesome movie even today...
And yes, focus on humans is the second biggest problem.
And the third problem is that the plot is just retardedly dumb and motivations/actions make no sense.
Example - So Sentinel Prime and Megatron teleported 100s of decepticons to earth...and plan is to get Autobots kicked off the planet and then send Shia Lebuf with a robo spy wrist watch to try to find out what the plans of 8 autobots are once the space ship launches taking them of the planet. Lets NOT just send 100s of decepticons we just teleported to attack the autobots and destroy them to little bits.
I know michael bay or whoever wrote this thought it would be dramatic to blow up the space ship last minute and all...but actions absolutely make no sense what so ever.