Rock of Ages is fine, but it could have been executed better. It's worth checking out for the price, but only if you can find somebody to play with.
The aim of the game is to break into the keep at the end of your enemy's path. The kind of lame thing is that it always takes three strikes. It might take more if you're especially terrible, but it'll never be less. So basically you'll always want to launch your ball as soon as possible rather than spend some more time building your defenses, because that's never a better use of your time. It's very fast paced but not very strategical as a result. The ball rolling is pretty simple and easy too, not nearly as challenging as a game like Super Monkey Ball.
Bulletstorm is pretty fun. I finished the campaign, at least. The final boss is a QTE though, which is really stupid.