This was my favorite of the three Michael Bay movies. Still too long and too many one-liner, comic relief attempts at dramatic points in the film. A real plot this time that has some interesting twists and tie-ins with the Cold War space race.
As a G1 TF fan, not too many complaints. I wish Shockwave had been more cerebral and less attack-tapeworm, and that Optimus wouldn't have uttered "please..." at one point, asking for mercy.
Excellent special effects as always, especially with the Chicago destruction scenes. The 3D was enjoyable, though I would think for the price you could keep the 3D glasses.
If you mostly liked one of the two previous films, you'll get something out of this one.
Overall, it met my expectations. I believe the writers tried to appease the hardcore fans with a lot of random add-ins, but it might have all been too much. Some of the characters were a bit stereotypical. Some new Transformers seem under-utilized (Soundwave, Devastator). If you go in with patience (very long movie) and average expectations from the plot, you'll still enjoy it and be impressed with the visuals.