Not quite ten years, but I've been playing Dungeon Fighter Online for all six years (plus some change) of its re-launch and about nine months of its previous incarnation. why? Because name me another MMORPG where you can use freaking fighting game inputs to do your skills. Source: about 3 years ago

In Dungeon Fighter Online, there's an old-ish epic accessory set called Refined Otherverse Magic Stones, which gave pretty good damage for its time (level 85 cap) and a pretty nice cooldown reset effect. The problem with it is that one of the pieces of the set inflicted Confuse on you as long as it was equipped, flipping your controls around. People who wanted to use this set had to get used to that. It was... Source: about 3 years ago

See also Unity of Command which used a combination of pygame and some homebrewn python graphics code if I remember correctly. Source: almost 3 years ago