Above anything and everything else it's the item scaling. Found a legendary artifact? It's now permanently nerfed because you found it at a low level. Out of everything else, that had to be the biggest gamebreaker for me. Then next thing would be specifically the monster level scaling. Instead of making the boss monsters stronger and stronger, or different tiers of the same monster (like wolves) why not just make a different breed all together? If the player reaches level 50, then there should still be those insane dragons that were impossible to fight at lower levels. The third thing was monsters appearing based on your level. How about different dungeons or areas in the province that are more dangerous than others? The entire
concept in leveling up is to be able to defeat the toughest enemies by the time you're done. Whenever I personally play rpgs, I aspire to become as powerful as possible to give me the greatest advantage possible. tes games allow you to do whatever you want whenever you want, so I initially plan out my class and then slowly work my way up at my own pace.
So I guess that's all I truly care about. The leveling system in Oblivion is complete rubbish. There may be other things about the game that I was unsatisfied over, but I can live with it.
Actually, I would like the stealth system improved as well. Psychic guards were annoying. It would be cool if there were different steps that the npcs would follow before getting caught. These steps took some time depending on a few variables. The steps would begin as soon as something happens to them. If they were attacked, how fast do they react to it? Does that particular npc roll over crying or notice where the arrow is coming from? If they quickly turn to see where they were shot (or possibly stabbed) can they describe what they are seeing to a nearby guard? Perhaps different articles of clothing could help them identify who you are or possibly make it harder to describe you. After they take the time to inform to the guard the description of the attack or attacker (if they get away) then the guard would look for someone based off of what they have been told. Another scenario is if a guard is nearby and sees someone impaled by an arrow. He would rush in to see where it came from and investigate. If you're nowhere to be found then you may have gotten away.