Out of 15 since I'll have a few games in certain slots:
1. Chrono Trigger/Tales of Phantasia/Final Fantasy VI/Seiken Densetsu 3 - A quad-fecta? at the helm which I simply cannot break. These are the games that got me into video game studies, through their sheer innovation and depth at the time (though I have yet to find a game to rival CT or FFVI in terms of sheer depth or ToP/SD 3 in unique battle systems). If you've never played any of these and like RPGs, then you are doing yourself a disservice.
2. Goldeneye - I haven't wasted as much hours on a game outside of this. Revolutionised FPS games on consoles. Getting the Facility Invincibility cheat is still one of my prouder moments with video gaming. Need I say more?
3. The Legend of Zelda 64 - Completing this shiny gold game through for the first time and reliving all those wonderful dungeons and bosses was truly a great event. While Link's Awakening and A Link to the Past are also quite awesome, this really showed what you can do with the LoZ series, and has set a precedent for quality and attention to detail.
4. Tetris - Mobile gaming has come a long way, with touch screens, cut scenes, and whatnot, but fiddling around with the big clunky Gameboys of old was just pure win.
5. Jet Force Gemini - Probably a little known game on the N64, this game came out near the end of the 64's lifespan but really pushed what to expect from adventure games. Massive landscapes, great character designs, and a robo-dog with rocket launchers.
6. Action Quake 2 - A mod, so technically not a 'game' but this introduced me into the manic world of online FPS games and it was a game where people died when you shot them. Something thats become more and more difficult to do of late.
7. Metroid Prime - Seeing the visor fog up for the first time....and the sparks from the gun battles, and the sheer isolation you felt brought memories of the old Super Metroid games rushing back.
8. Lylat Wars - DO A BARREL ROLL.
9. Dawn of War / Company of Heroes / Age of Empires - I hold these games above the Blizzard made ones purely because they were exceptions rather than the very highly polished and quality 'rule' of Blizzard games.
10. Diablo I & II / Starcraft / Warcraft - I hold them all in the same regard, great games and really hit the nail on the head in their chosen gameplay. Not really revolutionary but very well polished.
11. Rez - A very simple 'music' game, but one which is highly addictive and unique in its gameplay. I'm still hunting for the 'vibrating' add-on and a girlfriend to play it with though...
12. Pro Evo Soccer series - Just gets better and better, precision, realism and everything you really want from a sports simulator. Saw the Wii version was out, and keen on finding out how that plays with the wii mote.
13. Messiah/Wipeout/Silent Hill/Chrono Cross/Guilty Gear - I credit these 5 games with some of the best uses of music in videogames, one of my research/personal interests. Messiah showed a very awesome battle/passive transition which has become the norm of late, Wipeout introduced the commercial world to video games, Silent Hill and Chrono Cross soundtracks I could just leave on as ambience and fall asleep to them for hours on, and Guilty Gear...well Daisuke Ishiwatari directed, created, coded, voiced AND composed the music to this series. (Not a fanboy or anything).
14. Metal Gear Solid (PSX) - the definitive interactive film/game. The top down view was something I wasn't expecting when I first played this, and the story was pretty epic. Great use of sound and visuals to create a truly immersive story on screen.
15. Killer Instinct - While Street Fighter, Tekken, and King of Fighters take most of the attention, I have a special place for this great game. Not only were the graphics quite amazing for its time, but the gameplay and combos on the console were just so darn insane, but once you got into the swing of things, melting faces with Fulgore just reeked of win.