I liked Skyrim better vs Oblivion in most parts and there are some parts i like better in oblivion, overall, Oblivion (vanilla) felt more like a beta compared to Skyrim imo (considering Oblivion was one of the early games of the X360). Morrowind felt more complex and deeper imo but was never a big fan of the combat (never really finished Morrowind that time since it destroys my PC lol slowdowns and glitch galore).
Oblivion can shine when its equipped with mods, i had dozens (hundreds?) of mods running at that time, custom textures, new locations, new quests, godrays(!!), ingame SSAO, creaturer mods, stealth overhaul and thief/crime mods, custom animation mods, combat mods...list goes on.
Would like to see the return of the popular mods from oblivion to this game;
Martigen's Monster Mod; barrage of improved variety of enemies, smaller variants and larger variants of enemies and creatures (i want a super giant that can justify your trip to space when he hits you!)
Midas Magic (already previewing and is now available in Nexus for download!)
Better weather effects (strong violent thunderstorms!)
Mayu's Animation overall (you will have your own unique set of animations, particularly in combat),
Unnecessary Violence; use anything to do damage, throwing stuff, throwing knives and people(!!), kicking, using bread/shovel/stick as weapon, taunting your enemies, modifying your weapon grip, locational damage(!!) etc.
Deadly Reflex; Dismemberment (not just decapitation) and horse combat (discontinued i think)
Thieve's Arsenal; ropes for climbing structures, stun arrows, stun baton, water arrows (arrows that can put off torches/fires and therefore improve sneaking).