I'll just add to the general consensus. Don't expect plot. Don't expect deep characterizations. And be prepared for a few clumsy scenes and cheesy speeches.
But all that said, if you're going for spectacle, for some truly impressive action sequences, for several "holy crap!" moments, and for special effects that are truly revolutionary...
In other words, if you acknowledge that you're going to see a Michael Bay summer blockbuster based on a cartoon based on toys...
The movie is fantastic. I had a blast and a half, and I'd be willing to see it again while it's still in theaters.
(And of course it's going to be a blockbuster. As everyone knows, the primary ingredient for success is to have Hugo Weaving talk smack about the human race. And of course, Megatron does just that, ergo...)