* Best char gen in the series. Advantages/Disadvantages.
* Nice variety of guild quests: Dark Brotherhood, Fighters Guild, Mages Guild, Thieves Guild, Knight Orders, Templar Orders, Vampire Clans, Witch Covens, Daedric, plus many optional quests
* Variety of travel options: including horse, cart, and a choice between reckless or cautious fast travel
* Imaginative, hand-crafted landscape
* Wonderful cultural differences. Architectural diversity that reflects those differences.
* Fascinating, ambiguous, well-written main quest
* Bare-bones beginning (off the ship and right into the game)
* Text dialogue
* Cities in the world, not in separate world spaces
* All NPCs named (aside from guards), many with personalities and stories
* Static, but leveled enemies
* Dungeons do not respawn (good for those who like to use them as player homes)
* No invisible walls surrounding the game world
* Some of the most gorgeous music I have ever heard in a video game
* Ambient sound effects - no ther Elder Scrolls game has done thunderstorms as well as Morrowind
* Characters shield their eyes during storms - nice touch missing in later games
* Apparel options. Can wear clothes and armor at the same time. Footwear, handwear, pauldrons separated, can be equipped independently.
* Khajiit and Argonian digitigrade legs
* Raspy Dunmer voices
* Three disease types
* No essential NPCs
* Can drop quest items
* House strongholds
* Fatigue matters a lot for many activities, even when bartering
* Chance of failure in spell casting, potion-making, ect
* Real-time lock picking (and character-skill-based)
* Character skill matters more than player skill, for many actions
* Guild skill level requirements
* Quest directions in dialogue, journal
* Three separate weights of armor
* Deep, interesting underwater areas to explore (I adored grottoes)
* The UI. One-click-to open, re-sizable, movable, menus. Fog-of-war map. Map dynamically updates when you install or uninstall any mod (or official expansion). Best menu design in the entire series.
Oblivion
* Landscape a nice mix of procedural-generation and hand-crafting. Colorful, gorgeous, relaxing. My favorite game world in the series
* Again, music. Gorgeous music that evokes the pastoral feel of the landscape perfectly
* Physics
* Good voice acting (though fewer voice actors than were hired for Morrowind *sigh*)
* Face gen technology (say what you will about "potato faces," 200-position sliders could be surprisingly flexible)
* Some of my favorite animations in the series
* Unintentionally hilarious random NPC banter
* Improved sneak system
* Fame/Infamy
* Poisons
* Player activated blocking
* Ayleid ruins. The most beautifully-designed dungeons in the series
Skyrim
* Another gorgeous, hand-crafted landscape
* Nicely detailed, atmospheric dungeons, often with interesting stories
* Smithing
* Dual wielding
* Marriage, families, children (and playing games), wood-chopping, ect. Finally, a few activities that do not involve mindless killing
* Improved 3rd person gameplay
* Protected NPC status
* Mounted combat
* Enemies warn player away before combat
* A chance to oppose the Empire, for once
* Discovering alchemical properties via testing, using stations to mix potions
* Dragons - finest creature animations (and modeling) Bethesda has ever done
* Improved loot and enemy leveling and scaling
* The most attractive face and hair options in series
* Most attractive armor and weapon options in series
* More sophisticated system for skill gains. Value of object crafted or sold, damage done, ect, is a factor now