I'm in the middle of what's probably my longest Oblivion playthrough since 2008. My Steam stats say I spent 82.6 hours on the game and I still haven't finished half of the quests in it. In fact, that's kinda the problem. My char is a level 34 Spellsword, who's mastered Blades, Destruction and Heavy Armor. I've beaten the main quest, mages guild, arena and several, but not all and not the most interesting, city quests. But doing all of the other factions when I'm the Champion of Cyrodiil and when even ghosts recognize me as the Grand Champion of the Arena doesn't feel right. On the other hand, I put a lot of time in this character. So... I don't know whether I should start over or not.
I don't use mods, the only esps to grace my folder nowadays are the UOPs and a couple of other bugfixes.