Just saw this last night and I have to say that the film really has some great story ideas, but unfortunately they're undermined by a lot of out-of-place humor bits. After the lights came up, two of my friends said they enjoyed it, but they wish they had introduced the characters and I agree. The robots generally just appeared and did a scene and then did little cameos later. Only the "big players" such as The Fallen, Jetfire and Optimus really got good screen time. I think giving the robots a bit more identity would have helped the story immensely.
That said, visually this movie was amazing. Bay really knows what he's doing with battles and explosions. The sheer amount of military hardware should make any geek happy and the CGI on the robots was spectacular. Devastator was just an amazing sight to behold and Sideswipe is pure awesomeness. I was happy to see a lot more daylight interaction between the robots, giving us a much clearer look at them.
Overall I gave it an "Above Average" thanks to the stunning visuals and the core story, which I think does a good job of deepening the Transformers movie mythos.