I've watched the first two film this week to remind myself of events ready to go and see DotM. The first film is genuinely very good. Yes, the human characters are a bit annoying (though I find Shia far less annoying than most it seems) but it's a very entertaining film.
RotF is a bit of a mess, in terms of story and scale, introducing characters and plot devices never hinted at in the original, nerfing Megatron and reducing him to the role of henchman, and having "funny" bits that were clearly aimed at thirteen year olds ie the leg humping scene and Jetfire saying "bugger" or "bollock" every five seconds. Also Megan Fox really can't act. She seems to pull the same tortured expression throughout the film, and her only real purpose was to give the same thirteen year olds previously mentioned something to fap to. Despite all of that though, I still enjoyed it. It's not a patch on the first film, and you can pick holes in it a mile wide, but it's damn good fun and the forest fight is the best fight of the first two films in terms of choreography, even if Prime was stupidly overpowered given how easily he went down against Megatron the first.