More so than the first film, Transformers: Revenge of the Fallen is all about the robots.
In a nutshell, 2007's Transformers set up the story of the Autobots versus Decepticons, and then served up a semi-decent plot along with a whole lot of action. The Decepticons want to blow up our sun, the Autobots want to protect us, the Army guys are fully behind the Autobots, Sam Witwicky is at the heart of the problem/solution, and there's a government idiot who tries to block the good guys from helping us fight the bad guys.
Transformers: Revenge of the Fallen is what it is: a big-budget spectacle with an incredible amount of action, a frivolous plot, and one hot chick. The robot on robot fight scenes are fantastic (even if you can't tell who is who), the visual effects are absolutely terrific, and the sound effects will nearly have you bouncing out of your seat.