I decided to see this on Tuesday night sort of against my better judgement.. heck, I was at the theater already having just seen the much better X-Men: First Class and I had no other plans for the day... and it was really cheap ($7 for the 3D version). I was still disappointed, mainly because I had heard that it was so much better than the others in the series.
Bob covered all the main points, but I have a few things to add.
1.) No one likes Shia Lebeouf. Yet, the whole pretense of the first 3/4 of the movie is that we're supposed to feel sorry for him because he just doesn't get the respect and hero worship he deserves. Sorry, Mr. Bay, putting yourself in a movie as a proxy shouldn't be this blatantly obvious.
2.) This movie has absolutely no sense at all of tone and consistently. There is action, but it's blah and samey, with only one really cool moment (The honestly sweet Optimus on Megatron Fatality at the end). There is drama, but it's terrible and has no impact. There is comedy, but it's probably the worst and least funny comedy that it shouldn't even be called by the name. As if that wasn't bad enough, there is absolutely no sense of transition or timing in any of it. You will get whiplash as the "film" jumps from terrible action to terrible comedy to terrible drama to comedy to action to etc. Despite all of the other negatives about the movie, this is really the worst aspect of it.
3.) Rosie is ass ugly. Sure, Megan Fox was only sort of hot in that overly polished made for Hollywood and/or an Adult Film career way, but at least she has a genuinely attractive look, especially to her face. Rosie is just ugly. She has a nice body, sure, but I dare you not to shudder any time you see her face in this movie. I don't know if it's the make up or what but.. *shudder* Normally this isn't something I'd comment on in a movie as it really shouldn't matter, but seeing as she is so blatantly positioned as "da sex bomb" (and, near honestly, the only female) in the movie, it needs to be mentioned.