Wolfenstein 3D free through browser.

http://wolfenstein.bethsoft.com/game_NA.php

I like the concept of the game, killing Nazis, but I never was a huge fan of the FPS genre. I didn't like them at all until I played Quake MP, Goldeneye, Perfect Dark MP, and then Unreal Tournament MP. I played the game and finished level 1, floor 2, on the highest difficulty before quitting. Didn't really enjoy it at all. It's a classic, sure, but being the only game out there at the time doesn't mean it's any good.