This is a surprisingly excellent game considering it's based off a movie. I usually tend to avoid games based on movies because, well, most of them are pretty bad. Transformers is one of the few exceptions. The controls and gameplay can get rather frustrating at times, and yes, the missions can get repetitive. But in terms of smashing things, blowing stuff up and going toe-to-toe with robots on the opposite side, there's plenty to enjoy. It's a lot of fun.
Another positive point is the alternating between mission mode and freeplay mode. When you're not in the middle of a story mission or a challenge mission, you have free reign to run around (or drive around or fly around, depending on your character's vehicle form) the mission areas and do pretty much whatever you want, which is awesome. Watch out for rival transformers and humans who are just a little over-protective of their property, though.
As for the story, it differs very slightly from that of the movie. This is mainly due to it focusing much less on the human stories and playing out more from the robots' perspectives, and that is definitely a plus. It's a pretty simple plot, but it's epic enough to be entertaining.
The graphics are also very good. The robots and level environments are pretty well detailed. The humans don't have much detail, but who cares about them, really?
So all-in-all, there are a few bumps here and there, but it is otherwise a very decent game. Worth buying if you're a fan of the movie.