Like a lot of ACE games, Rock of Ages is a diamond in the rough, and well worth the price of admission (especially how often it's on sale and how deeply discounted).
The premise is fairly simple: you roll a giant boulder through an obstacle course trying to mash in a set of gates at the opposite gate.
It has a great sense of humor, interesting graphics, and mechanics that are at least something different.
In my opinion the only downside is the combination of building defenses for your opponent along with trying to run through theirs: you can only place obstacles while you're waiting for your next boulder and this is also the only time you can try and pinpoint-catapult the enemy. Annoyingly, the computer opponents in single player seem to be able to catapult you the entire time (because of course) and have ridiculous accuracy, which can be frustrating.
So it's not perfect, but it's often only a few dollars, and is easily worth that, if not quite a few more.