I only get to pick 3?? This will be tough.

1. Ultima Online. This game did what WoW fails to do with every new patch, which is have a completely level playing field for pvp. No imba classes, no gear giving massive advantages, just unadultarated skill throughout.

2. Goldeneye 64. Incredible single player with amazing longevity and some exceptionally frustratingly hard challanges. Multiplayer was a cut above anything in it's day, and even now when I have my mates round we'll pull out the old N64 and have some games of One Shot Kills, Pistols only, in the Library.

3. Gauntlet 2. This was groundbreaking stuff. A top down real time combat rpg/beat-em-up that you could play with 4 players simultaneously on the original NES. Early levels, so much fun, but later levels you needed a degree of teamwork and coordination that probably didn't come around again in any games until everquest almost 15 years later.