I agree! I loved the first Transformers. But the second one...ugh! The only thing I liked in that movie were the amazing special effects on the robots. Anyway, here are the reasons, it sucked:
1) Michael Bay did not follow the original script/story that screenwriters Orci and Kurtzman laid out.
Here's what they said in an interview: "We were very surprised when we saw it, too, and it’s a choice that was made. If anything, it just shows you that we don’t control every aspect of the movie."
2) Production was rushed to meet the premiere deadline.
3) Autobots got shoved to the side for more extended human drama & military action.
4) Too much attention spent on CGI at the cost of crafting a good story or character development.
5) I really think Steven Spielberg (exec producer) had a hand creatively in Transformers 1. I guess he was really distracted by other things during the making of the sequel.
Shia Labeouf sums it up perfect: "We got lost. We tried to get bigger. It's what happens to sequels. It's like, how do you top the first one? You've got to go bigger. Michael Bay went so big that it became too big, and I think you lost the anchor of the movie."
I suggest viewing Transformers 3 with very low expectations.