Sadly, there still are a few dealbreaker apps that prevent me to switching to Linux.
There's also the massive back catalogue Windows has, my girlfriend loves playing random PopCap games and other casual-friendly stuff that are not yet click-and-play in Linux - was going to say "not available" but Google has an installation guide for Wine, but not yet available to mainstream users.
I expect they'll probably arrive soon, since all the Humble Bundles have been Linux-friendly for ages, but they don't have the games available now. They're probably trying to get the client more stable, I guess.
Seeing mainstream support (Steam and others), and 62 titles shows Linux has gone a long way, and of course the rise of web gaming is a huge boon.
Just not on Linux Steam, yet.
Probably still the best games on Linux imho...
I don't like First Person Shooters (even the original Wolfenstein gave me motion sickness, and I don't have great motor skills), that's why I forgot about those.
I've always liked turn-based strategy games, or real time strategy games (at medium or slow speeds, I get destroyed on online matches), puzzle games, point-and-click graphic adventure games, etc... and I distinctly remember searching for those and not finding much back then.
I definitely need to give Linux another try, but I don't manage to convince myself to set aside the time (it might be a good investment, though :) )
Sid Meier's Alpha Centauri is a favourite of mine, not sure how easy it is to get a copy of these days though.
DEFCON, Darwinia: http://introversion.co.uk/
Wesnoth is a great turn-based strategy game and has an unusual amount of polish for a FOSS game.
SpringRTS is a really fun RTS, if you can look past the many bugs in the launcher/lobby: http://springrts.com/