The original Prince of Persia, Another World, Cho Ren Sha 68k, Spelunky, Operation Flashpoint, DooM and DooM II and Halo 3 rank among the essentials, for me. And those are just the ones that spring immediately to mind and I'm most liable to play often.

There's also a whole host of arcade and indie games I really find myself digging into.

Bioshock. I've played and beaten it 16 times and counting and it's only just starting to get old. After that, Halo3

I spent countless hours playing Morrowind for the Xbox and even more time on the PC when I finally got a decent gaming rig. Morrowind is without a doubt my #1 single player rpg of all time...As far as MMOs go, Phantasy Star Online and PSO:BB have always been my favorites...Started on the Dreamcast, went to Xbox, then found a schweet and pretty well populated private server for PSO:BB. To think it's been around for 10 years and there's still an active community playing the game, not to mention all the people coming back to it for nostalgia value which is how I found the server in the first place. For anyone who has ever liked PSO and would like to join the private server, check out . The more the merrier!

I second Morrowind, I love making mods and whole cities with the editor, not to mention the mods available on the net! plus the atmosphere ingame was amazing, I remember my first thunderstorm while tracking through the grasslands and it was awesome!