To be honest, I'm relatively happy with the combination of FOSS games, indie games like in the Humble Bundles, and older commercial games like Doom 3 and Wolf-ET such that gaming solely in Linux wouldn't be an issue for me. The problem, however, is a question of effort. Let me list one example:
- Doom 3 -
Windows:
* Install game
* Patch
* Play
Linux:
* Install using the latest Linux installer using the text interface (which was only supposed to be a backup in case the GUI works, which it doesn't anymore because it was built to use the GTK1.2 libraries which don't work properly/aren't available with modern distributions).
* Copy the required .pak files from the game's CDs to where the binary is installed, because the official installer won't do it automatically (though it's possible someone's written a script to do this by now).
* Run, then find out there's no sound because OSS was deprecated in modern Linux distributions. Spend an hour googling and trying different options until you find out the correct method to launch D3 with sound:
doom3 +set s_alsa_pcm plughw:0 +set s_driver alsa
* Create a .desktop file/link because the installer fails to do so properly, otherwise you don't get a shortcut in your DE of choice.
* Play, then discover you have massively jerky framerates because the Linux kernel changed to use a different method of timing (too complicated for me to understand) which affected how Doom 3 determines timing. Fixed using this additional variable during launch
set com_fixedtic 1
* Play and enjoy the same game that worked with far less effort in Windows.
Sure, half the problem was in iD not giving a crap at producing a good installer that would do most of the work for you (like copying required files) and not using static GTK libraries that would survive changes to distros. But things like the removal of OSS within the default builds of distros as well as the change to kernel timings, kinda do make a few problems for older games.
Newer stuff tends to works better, but often there are quirks even in newer Linux ports (I won't keep listing stuff but there are a number of complaints about bad Linux ports of a number of Humble Bundle games - look them up). For gaming, I get tired of messing about when things just fucking WORK in Windows. It's suppose to be entertainment and escapism after all.