I watched the first two Transformers films again in anticipation of this. I have to say that the second wasn't as bad as I remember, apart from those annoying racist stereotype robots.
As for the third film, it was good, but far from perfect. I watched it at imax in 3D, and it was one of the better 3D films I have seen, I would say I like the 3D effects more than Avatars.
Transformers 3's main failings are that it is badly paced and far too long. Also it lacks both action and transformers in the first 90 minutes. The film focuses on Shia LaBeouf far too much for my liking, especially the first half, which doesn't even feel like a transformers film. If anything I would say that I felt as if I had watched two films by the end of it, the first 90 minutes being a comedy and the last hour an action flick.
The first 90 minutes had genuinely hilarious moments, but it didn't feel anything like a transformers film, at times I even forgot that's what I was watching. I think if 30 minutes of comedy had been cut out it would have been better for the overall film. The transition between comedy and action film was really abrupt, which made it feel even more like two films for me. And by the last half hour I just felt drained.
Also the addition of Sams new girlfriend, played by Rosie Huntington-Whiteley, felt really unnecessary. She is even more redundant than Megan Fox's character, and I will even go as far as to say she is a worse actress than Megan. I just found her really unconvincing in every scene she was in. I don't think transformers needs a female lead who when the action starts, does nothing but run around and look worried.
Like I said overall I think its a good film, but Michael Bay just did a really sloppy and self indulgent job. The film would have gained a lot with better editing to reduce its length, and it really needed more action scenes and less Shia comedy hour in its first half.