I voted 'almost never', but its not that simple. I'll go long stretches without playing games then have short stretches in which I play them a lot.
Dwarf Fortress is a current favorite. Its an odd thing... Its vaguely like simcity simulated down to individual-person level, and by "person" I mean "short, angry, and flammable".
It is still very alpha, and it shows. The interface is somewhat inscrutiable, and its quite buggy, but the bugs are usually metagame errors and hilarious: "flying creatures give birth in midair, leading to tragedy", "mayor ordered himself beaten for failing to make crystal glass", "goblins teleport to capture location on fire when dropped in lava", "amputee liason leaves an extra sock and shoe on the map edge whenever she arrives", and so forth.