Doom was the first shooter I played properly, as in I clocked the entire game. I did play Wolfenstein at one point but, ehh... I'm really into oldschool games and generally don't care about graphics all that much but it looked so bad even by my standards that I really couldn't enjoy it for long (well, it probably wasn't the graphics as much as the fact that all the corridors were more or less identical... either way I didn't have fun).