I don't know which are the most played games outside linux, but I am sure "Battle for Wesnoth" made itself the most tried/played game in Desktop Linux history yet. Doubt? Talking about id games?
Let's watch http://pyweek.org
Actually, I can make a database query to get top-10(20, 30) of most viewed pages on LGDB, if you are interested (and if pheonton doesn't mind).