You just killed a demon prince and are Arena Grand Champion, but you'll find out any lame npc guard will kick your ass.
In the beginning I thought it was awesome, I would go around the cave sneaking and doing 1 shot kills and it felt oh so good. But now I'm starting to skip the boring dialogue, I'm noticing I need 20 arrows to kill trolls and goblins (it's ridiculous, I'm running around and shooting, where's the "sneak" in that? My sneak attack does maybe 10% damage), I'm noticing I can barely pick up anything because I have low strength, I'm tired of traveling so I just double click the map.
Oblivion could have learned:
From Shenmue -> City life kinda sucks in Oblivion. The bases are there, but where are the children? Where are the cows and chickens? Why are there so little bystanders! The Imperial city is almost deserted. If you're gonna bother to do it, at least do it right.
From Fable -> Fable makes such a good job at quick quests. No going to A and B and then A again and then C and then look for person D and then find document E and take it to A who is 2 frigging towns away and then go to cave F and kill everything, recover the ring, bring it back to A. In Fable you get the quest, you do the deed, you collect the reward.
From Thief -> Sneak is great and all, but some environments don't help at all. It'd be cool if you could put lights out and the sneak factor wasn't just based on a skill number.
From Dungeon Siege -> Wow, is this where current RPGs and Online RPGs are going? 1 on 1? God forbid you "aggro" a second monster or else you're dead! I wish we could have a lot bigger battles in Oblivion and not "always" the 1 lone monster patrolling the hall or the final boss who is just waiting for you "alone". More like Dungeon siege or Might and Magic with huge amounts of monsters coming at you would be an improvement.
In conclusion, at first it'll be great, then it'll be boring and you'll be skipping all the dialogues and cursing the fact that you're arena Grand Champion and just beat one of the princes of oblivion quite easily, but a bear, a mountain lion, brother Martin or any of the Blades will still kick your ass.