I've only played Morrowind Oblivion and Skyrim... and I played them in chronological order (as they were released)
I played the console versions of all of them, but I also played the pc version of Morrowind.
Graphics: Skyrim, Oblivion, then Morrowind
Weapon Type Variety (axe, bow, crossbow, sword, longsword, katana, etc.) : Morrowind, Oblivion, then Skyrim
Weapon Skin Variety (steel, iron, dwarven, daedric, ebony, etc.) : Skyrim, Morrowind, then Oblivion
Companions: Skyrim, Oblivion, then Morrowind.
Gameplay: Morrowind, Skyrim, then Oblivion
Combat: Skyrim, Oblivion, then Morrowind
Story: Skyrim, Oblivion, then Morrowind
Exploration: Morrowind, Skyrim, then Oblivion
Music: Morrowind, Skyrim, then Oblivion
Decorating your house: Oblivion had the nicest houses, and the best decoration....but nothing really to put in them, except a handful of things. Morrowind only had 3 houses, they were all really nice..... but you don't get them until the end of the game.... instead, most players just made their own home by killing NPCS, which was awesome. Item placement was poor.... some items like books just had to be stacked, and couldn't be put on a shelf in a traditional fashion. Skyrim.... lots of houses to buy..... but the item placing mechanic was terrible. Made decorating really really hard.
Freedom to do whatever you want: Morrowind only. When they took levitation and jump spells out of the game, a small part of me died. They also added non-killable npcs to oblivion and Skyrim... :(
Difficulty: (without moving difficulty slider) All the games start out okay, and after a while you become invincible.
Morrowind, though, was the toughest to get the ball rolling in... just because the combat system was balls.
Overall Fun/Favorite game: Morrowind, Skyrim, then Oblivion
I think the determining factor is the fact that everything in Morrowind was hand-placed.
Every cave was made by a person, not generated.... Oblivion lost a LOT of points here.... many caves/areas feel generated, and had random scaling loot rather than legendary artifacts.
The cool thing about Morrowind is that if you know where something is, and you are skilled enough to get it, then nothing (level cap, invisible walls, etc.) can stop you. You could run through an end-game scale dungeon with an invisibility potion and snag some epic loot before even hitting level 2!
There was one door (if i recall) that required a key to open in Morrowind.... everything else could be picked.
You can even beat the game legitimately (without glitches) in 7 minutes