Tower defense + hack and slash + crazy huge amounts of monsters? Yes please.

Did you play Fallout 3? If you did, imagine that, but scarier, supplies are limited, and the HUD... is cleverly implemented, with more horror. Think Dunwich building, but the whole game.

If you didn't: Metro 2033 is a great game. It's survival/horror, and supplies are rare and cleverly hidden. There were several times playing when I almost jumped out of my seat (of course, playing in a dark room at night doesn't help), but Metro actually -feels- scary. The environments are detailed and the world is very immersive. Play it if you like survival/horror, Fallout, or anything post-apocalyptic. Just prepare to deal with Russian accents the whole game.

Cyberpunk meets philosophy in the prequel to the Deus Ex series. Now, I haven't played the first 2 Deus Ex games, so I can't comment on how true HR is to the series, but as a game it was quite enjoyable and thought provoking. The plot was nothing new, but the concepts and differing ideals espoused throughout the game certainly will have me thinking for days to come. As if that wasn't enough, the gamplay is fairly varied. There are usually 3 or more ways to get to an objective, and you never have to kill enemies in the game, excluding bosses.

TL;DR: It's a good game, and if you like philosophy/cyberpunk, why haven't you played it yet?