Woohoo!Was Steam-only, and many people bugged them on the official forums to release on Impulse. Though I think it was just a contract timed exclusive thing since none of the devs ever commented on it, so they were keeping quiet until that expired.
Anyway, you can check out a review
here. For $20 I'll probably end up getting it (along with World of Goo and Age of Booty). Its kind of strange that Gamespy is the only place that has reviewed it.