Descent 1 and 2 are classics of the first-person shooting genre. While they were not best-selling games upon release, they were the first true six-degrees-of-freedom games. Not many games have been made in the genre since (Shattered Horizon is the only recent one that leaps to mind) but there was a third, slightly less regarded Descent game.
This doesn't mean it is a bad game, though. In fact, Descent 3 holds up far better than one would expect, and shows just how much the developer matured in the time between the first two and the third.