Fair enough. If we are only considering vanilla, then Skyrim is by far my least favorite of the last three TES games. But full disclosure here, modded Skyrim is hands down my all time favorite game in the world. I won't play Skyrim without mods anymore (and I mostly only mod game mechanics), but I did play vanilla Skyrim for several years on Xbox and have also played at least 500 hours of vanilla Morrowind and over 1,000 hours of vanilla Oblivion. So I will base my answers on those experiences only, not my experience with a modded game.
I will focus on game mechanics rather than atmosphere, since that is what I am most concerned with (I liked the atmosphere from all three games) so I will let others discuss the respective differences in atmosphere and focus only on game mechanics.
My view is that Oblivion was an overreaction to the complaints that Morrowind was too easy at high levels, so Bethesda went overboard with world leveling and world scaling, which exacerbated issues inherent with Morrowind's character leveling system in terms of incentivising the player to chase attribute increases by "efficient leveling." In addition, Bethesda wanted to "streamline" the game to attract a wider base. So, we got a game with simpler game play mechanics, fewer skills and spells, no chance to "fail" (skill level only affects the strength of skills, not whether you can do something in the first place), an attribute/class system that did not work very well and over the top world leveling/scaling. But Oblivion also had voice acting, better sneak detection mechanics, better archery with arrow drop, physics affecting objects, more fluid combat mechanics, higher resolution graphics, etc.
With Skyrim, Bethesda continued the trends from Oblivion, but this time they did a much better job of world leveling/scaling. Skyrim's world leveling/scaling is more in line with Morrowind's world leveling, where you can meet high level enemies at low level and you will never see all bandits donning glass or all marauders donning daedric (bandits in daedric is a misnomer since bandits wear light armor in Oblivion, so you NEVER see them in daedric, but I digress).
Morrowind is actually a highly leveled world (the only things that aren't leveled are named NPCs, a few hand placed enemies, and hand placed loot). People forget that sometimes. Although I am a huge critic of vanilla Skyrim (and huge Morrowind fan), I view Skyrim's world leveling/scaling to be superior to Morrowind's world leveling. Skyrim challenges you with some high level content like Morrowind, but Skyrim's world leveling/scaling will challenge you longer than Morrowind's, which starts to get pretty easy by level 20 or so. Still, both games suffer from the issue of being able to outlevel enemies if you play long enough.
Anyway, if the over the top world leveling from Oblivion was what turned you off of it, you will find Skyrim improves that aspect quite a bit and is closer to the way Morrowind handled it.
Skyrim solved the character leveling by simply deleting attributes and classes entirely and replacing them with a pick your perk on level up system.
Bethesda continued the streamlining trend with Skyrim by removing yet more skills and removing a bunch of spells and spell effects and spellmaking, removing the ability to manipulate an NPCs disposition directly and removing many other things that many individual players held dear. They brought back enchanting but in a much more simple streamlined form.
Skyrim added in a few new spell types like runes and wards, but those are not implemented well in the vanilla game for various reasons. Skyrim made further improvements to sneak detection mechanics and combat is more fluid and quite enjoyable for me. Archery is further improved and quite enjoyable.
Overall, I prefer vanilla Oblivion to vanilla Skyrim because Skyrim removes too many features I find dear in its attempts to streamline the franchise for the modern gamer. But if you can get past the streamlining, you might enjoy Skyrim because it does quite a few things right, and world leveling/scaling is definitely improved over Oblivion.