JetSetDizzy
[11] Champion
If you know how to abuse the leveling system it is worth leveling, you just have to engineer three x5's where you want them each level.Oblivion - pretty much everything.
In that game, every aspect of the game changes according to your character's level. Yes, the loot available to you gets better as you progress, but the enemies become harder. And I mean every single enemy. Suddenly areas that had rats and wolves start to become infested with ridiculous mobs like minotaur lords. Whereas rag-tag bandits would be using rusty daggers and swords at level one, they magically have access to top-tier weapons and armor by the time you hit level 25. There is no benefit to leveling up since the game only punishes you for progressing. It is not only possible to beat the entire game at level 1, it's actually much easier that way.
Also X-Factor in MvC3.
It's still kinda dumb yeah but its hard to imagine how else they could do it when you can do anything iin any order and have it remain at all challenging. Games are supposed to get more difficult as you go so as long as you don't abuse the fact that you aren't forced to level the difficulty curve should be fairly reasonable.