Elder Scrolls IV: Oblivion

Oblivion is a fun game, but arguably worse for getting you distracted by side quests and faction stuff than Skyrim. Also the leveling system is a complete mess and I'd go as far as saying just plain broken.

As I remember (correct me if I'm wrong someone), every 5 levels all the enemies in the game jump 5 levels to match you. If this kind of stepped level scaling wasn't bad enough, the system is willfully convoluted, so if you haven't got your head around it it's really easy to level up badly and get comparatively weaker than enemies and NPCs the more you "progress". Leveling up optimally can include such awesome gameplay as jumping constantly instead of ever just walking or running, or repeatedly conjuring enemies just to hit for half an hour.

Skyrim fixed all that crap so you just level fairly naturally by playing the game like a normal person and pick perks that interest you. And importantly when you reach higher levels, you feel like a badass and don't get squished by some random bandit.