Bulletstorm. People assume that the only reason to buy it is to get in on the Gears 3 beta. But Bulletstorm (much like Crackdown and the Halo 3 beta) is a great game in its own right.
There is no online multiplayer other than Anarchy mode, which is players vs. AI rather than pvp, making it more like Horde mode in Gears or Firefight in Halo. But the campaign is a lot of fun, and there's this mode called Echos, where you go through certain parts of the campaign and try to score as many points as possible.
I will, however, say that $60 is probably too much for the game given the lack of pvp multiplayer. If you are interested in Bulletstorm and don't care about the Gears 3 beta, you can probably wait until there's a price drop for Bulletstorm. By then, any DLC should also be out.