The Wolfenstein franchise was always my favorite and is a great overall shooter. Hell, Wolf 3D is the grandaddy of all FPS games and even pre-dates DOOM. While Wolfenstein was never really that big on the story, the action is still there. I never seem to get bored of zapping nazi soldiers with the Tesla gun, turning them into mince-meat with the Venom or even burning them alive with a flamethrower as they dance in the flames. Also, I'm pretty sure that Wolf 3D is still the only game where you can actually kill Hitler.