Got this as a random in the Humble Freedom Bundle. Run and gun Serious Sam style in a procedurally generated tunnel maze. Variety of guns and powerups you can unlock, but really it's a game for killing a little time in quick runs, there's no larger story or campaign. It's probably not worth the $15 full freight, but if it went on sale for $10 or less and you like that kind of gameplay, it would be worth looking at.
--Jello Biafra: "If evolution is outlawed, only outlaws will evolve."