I play until I get sick of it. Most of the time, I don't hit the level cap. Though I was just a couple thousand points (not that much, really) away from a level 60 Shepard in one playthrough of Mass Effect my last time. It's so cruel, they made it impossible to get to 60 in one go with a character. I did every single mission, found every artifact, only killed a very few enemies in the Mako (never a Thresher, a Turret, or a higher class geth).
I have a level 45 character in New Vegas right now and it's pretty ridiculous. I have all but three skills at 100 (Melee, Unarmed, and Explosives. My first two characters used those skills, though). I'll definitely be taking advantage of the level 30 cap trait in future playthroughs.
Whenever I play Oblivion anymore, I don't get very far with a character. I try to keep them as a specialist and not a jack-of-all-trades. When I get sick of playing it, I strip my character and try to take out everyone in a city with my fists until they kill me. Then I leave the game alone until my fatigue of it wears off.