Oblivion works fine still. And of course a 9 year old game (released in 2006) on High / Ultra is going to look like a 2015 game on Low.
It can still look good modded though, but modding does need a lot of patience (as does Skyrim & Morrowind):-
- Install Core game
- Install Expansion pack (Shivering Isles) + DLC
- Install official patches
Start modding:-
- Unofficial patches (inc SI & DLC)
- Darnified UI
- HD texture pack (Quarl's?)
- Unique landscapes mods (Aspen Wood, Cheydinhal Falls, etc)
- Better water
- Brighter torches
- Darker nights & dungeons
- Clocks Of Cyrodiil
- No more annoying comments
- Natural habitat & natural vegetation
- NPC levelling mod
- Passive / more random behaved wildlife, etc
- Whatever else catches your eye / suits your style of play
Elder Scrolls games are not for the impatient, and I'm not even talking about playing them, but merely getting them setup just right.