Sin is a undervalued game. This is probably because it had to contend with Unreal and subsequently the seminal Halflife on release. It didn't have a chance. However, the game is good enough. The physics and the weapons a quite fun, and although the plot is pure hokum, its entertaining enough. It's quite long as well, although not quite to the degree of halflife. Picking it up cheap, I reckon this game is actually quite good for a laugh, but don't expect a miracle, and if you wan't to play the "old" classics, opt for halflife. If you don't aim too high this game might well entertain you and even surprise you.