I didn't really like the first two or the fourth. For some reason I really liked Dark of the Moon.
One of my most major gripes is how some of the most liked characters in the franchise as a whole die. Ironhide, Jazz, Ratchet, Starscream, etc. Along with the emphasis on the human characters, I mean, really, I went to see a movie about the bots, not the humans.
I'm not saying I hate the movies, I just dislike them for multiple different reasons.