I'm going to be honest. I thought it was just ok.
I am from the old school film theory where sometimes less is more.
I prefer movies that have... oh what's that called, PLOT! That's it. However, just the right amount of plot. Not too much, and not too little. I'm not saying that Transformers II did not have a decent story behind it, but I felt the first one was so much better than the second.
In the first one they took time to develop a story line and make you really feel it. In this one, they just kind of threw a bunch of new characters, tossed in an arse load of special effects, tons of explosions, and then peppered a few heart felt moments to keep the chicks watching it. There was no real character development. We didn't get a taste for the new autobots, except for the two "Gangsta-bots." Finally the constant action just made me start to think, "Sure that was kind of cool, but did it really add anything?"
The final straw that pushed this from a great movie down to just a good movie was the sequence when Sam meets the fallen's brothers, then Megan says she loves him.
"Sam, I love you."
"Oh hey! Good to see you again!"
Hmm... I can't seem to recall at least 10 other movies that have used that same concept. Plus the ending kind of pissed me off. "Here, let me kill myself so you can add me to your hardware collection."
In a nutshell, it feels like they sold out. They tried to pack it with so many different styles so it would appear to the entire mass market. As someone who loved the transformers (even though he was not a child when they first became popular), this just feels like they went away from what the Transformers was truely meant to be. Kind of disappointed given all the hype.