System Shock 2 is most likely the scariest game I have ever played, Half-life being the only close contender.  As good as HL is, though, SS2 tops it with more storyline and depth and personality.  I'm an RPG fan and I'd consider SS2 more of an action game than an RPG, but the game still allows you to configure your character in ways that deeply affect the gameplay.  First time through I played as a psionics guy who wielded hand-to-hand weapons.  Late in the game I was able to use an invisibility psi power, run up to enemies, and whack the bejeezus out of them.  I didn't have to use guns much, and when I did I just used the cheesy little pistol.  Next time I play I'm going to specialize in guns and be a long-distance sniper.  The role-playing elements are not that deep, but I still greatly appreciate the opportunity to choose how my character develops.  That's why this game is better than Half-life.