best oldschool arcade game: bubble bobble, for realz
best arcade game: street fighter 2 (and all the subsequent versions)
best fps: halflife 2. apart from the ending, this is absolute goddamn gold
best rts: starcraft with the broodwar add-on, hands-down the best-balanced RTS i've played
best scrolling shooter: ikaruga. simple idea, pulled off absolutely awesomely.
best MMORPG: i'm gonna have to say World of Warcraft. i mean, i've only played Everquest, Final Fantasy XI online, City Of Heroes, Guild Wars & WoW, but as far as i can see, FFXI was pretty much the best ever, and for me WoW has beaten it. they haven't done it with flashy graphics, they've done it with cool gameplay. i'm close to level 20, and for me it still mostly feels like a really good single-player RPG that just so happens to have these other dudes running around in it that you can team up with sometimes. i mean, ask me again in 30 more levels & i can give you a better comparison to high-end EQ gameplay. but so far it's got FFXI's 1-20 gameplay beat.