I was actually into video games bigtime when they came out. I rememeber the change from pinball to Sapcae INVAders, PacmAN, but my favorite OLd School game by far? Dropped mad quarters at the local pizza parlor. This is before you could play anyhting at home but Pong.
First multiplayer game I really played -- amazing game, wholly original, the first great console FPS.
Changed the face of video games forever. It's been outdone by the GTA games that followed it, but this is the original, and the most incredible for its time.
Best sports/football game EVER.
Best fighting game EVER.
I've wasted more of my life playing Halo (primarily Halo 1, but also Halo 3) than any other game.