I don't want as much new content as possible. There's plenty already.
The problem is the game has been out for quite a while, and certain aspects of it are still largely overlooked and certain features almost feel left partially unfinished.
I would like a big "quality of life" update that would improve and/or fix things the game painfully (in my opinion) needs and which people often asked for repeatedly (sometimes for years I think).
Heck, I would pay for it just as much I'd spend on a DLC.

List of things I can think of:

1) Better character models
The faces are nice. The rest... not so much. Certain parts of bodies have angular shapes, and the body texture is very blurry and low resolution, especially compared to faces.
For your viewing pleasure, one of my characters:




This shouldn't even need any comments, but seriously ZOS, it's 2017. The game came out in 2014 and this wasn't acceptable even back then! The texture quality difference between head and rest of the body is incredibly big. I don't want my characters look like burn victims. If the skin on the head can look decent, I want the rest of the character look the same.
And yea, nice boobs bro.
Seriously
(I fully understand performance is extremely important, and certain compromises have to be made, but not like this!!)


2) The crafting interface
Oh my, where to begin

• Preview functionality. We should be able to preview both armour and weapons. The camera should be zoomable, and we should be able to select the light intensity and direction, AND background (I simply cannot preview dyes half the time because it's either too dark or sun is in the opposite direction. Extremely frustrating!!). I would say, a toggle between current open world interface and "artificial room" where it would be possible to do all of the above would be great.
  We should also be able to preview any dye combinations. There's no reason why we shouldn't be able to preview locked dyes or styles. I'd like to know what things look like so I can decide whether to start trying to get them or not. Some of the achievements take enormous amounts of time and I don't want to grind something only to find out the dye looks bad!
• More user-friendly scrolling list of styles/mats/whatever. One neverending list is annoying, and especially since it's impossible to quickly jump at the beginning or the end.

3) Animations
The animations in ESO are pretty good, but I feel like some are simply missing. See my thread over here for details what I think could be added.


4) Character creation
Profiles. PLEASE! A way to save/load/export presets. A button to reset all sliders to default values.
I'd like to be able to partially create a character and come back to it later (sometimes I just can't come up with a decent name all of a sudden with character already done physically), without having to redo everything from scratch.
I posted a feature request here.
It's kind of related to my wish for character models to be better.


5) Loading times unrelated to player's PC or connection
Certain loading times are completely ridiculous and have nothing to do with what PC a person has, and everything with how the server side of things work.
For example, I regularly measure around 45-50 seconds between pressing "login" and landing on the character selection screen. There's no logical reason why this should take so long. There must be a hiccup or something somewhere. Nothing much is being loaded during this time on the user end. After that, I typically stare at "requesting character load" message for good 10-15 more seconds before I finally start loading. What was the game doing the previous minute??? Loading all the game assets doesn't take too long without addons with decent PC.

Zoning in and out of completely empy Ebony Flask inn's room with no addons active takes between 10 and 13 seconds. Why? There's nothing to load! Definitely not the second time at least! This should take like 5 seconds at most. I really question the optimization of the software that runs the game world and associated networking stuff.

Sure, you can troll me with "ololol, impatient, just wait blabla, it's just 30 seconds", but you just need to see the bigger picture. If the game is so inefficient that these loading times are so big, what do you think it does to say Cyrodiil? Oh wait, you already do.
Come on ZOS!

Or: there's no reason why _repeatedly_ zoning into an interior cell should always take more than say five seconds.
Again, I wrote about that before, see here. Some of the loading times I described

6) The cosmetic items system
I think this calls for a little bit of an overhaul of the interface.
It's absolute pain in the arse to check the appearance items out, because it's impossible to control the camera while having the collections window up at all (rotate and zoom in all the way to the face is absolutely necessary). The UI window obstructs your view (changing camera position in the options is unacceptable workaround). All the various hairstyles and other items should have miniature preview images instead of generic bust icons. I'd like to see a simplier single click to try/equip system (when you choose to use mouse for whatever reason).
edit: The cosmetic stuff should also be broken down into more subcategories. For example, head markings. This could be broken down into general tatoos, brows, lipsticks, etc. One huge is is not working too well.


7) Miscellaneous stuff.
An option to make all keybinds and game settings account-wide without having to rely on addons that get abandoned and stop working at some point.