I went and saw it last night and it was horrible. No plot, just 165 minutes of neat special effects which get boring after the first 30 minutes. I don't think I've ever been this disappointed that I paid money to see something.
My advice: wait until it comes out and get it from redbox so you can watch it while you play on Minetime or something and not really pay attention. Related note: Nicola Peltz omg http://upload.wikimedia.org/wikipedia/commons/1/1f/Nicola_Peltz_(soft_contrast).jpg
When the first thing you see is MICHAEL BAY even before TRANSFORMERS, then you know it's going to be stupid.
Transformers is only good for fancy explosions and robots fighting each other. A plot is basically non-existent.
The movie moves both too slowly and too quickly, as scene transitions appear to have been significantly shortened during the editing process. The problem is quantity in this movie. There are so many action sequences related to so many story lines that midway through an epic fight, you might find yourself wondering what started this \battle and what the objective is other than destruction for the sake of it.