For me, it's the music; the way there are almost always some blue mountain flowers near signposts; the little animals that pop up and show you the way when you're on a tricky road; the beautiful Dwemmer decorative art—those lovely urns, vases and golden metalwork; the courageous horses that will take on a dragon; oh, and the food that looks absolutely mouthwatering and hard to resist; breathtaking weather effects, foxes and chickens and rabbits (please don't kill them!) ...

• Insects (Butterfly, Moths, Torchbugs, ect) wish there were more and non-flying ones.)
  
• Fish (Salmon, River Betty, ect.)
  
• Race Appearances (Not really a small thing but I really do like them I wish playing as them were more unique but that's another topic.)
  
• Minor Dialogue (Stuff that's easy to miss like the guards being stationed to Riverwood and Delphine)
  
• Graphics (To me it's a small thing)
  
• Beards
  
• Detailed Items (Like how you can look at them and in the menu, wish they had a Player Screen with your character though.)

The open-endedness.

The auroras for sure, there are few things in Skyrim more beautiful than the night sky.

How the music changes when it's morning or dusk. Following streams' to see where I'll end up. Changing clothes/armour/gear for different occasions. Going out hunting in the night, silently chasing wild animals while staring at the moons.
Wandering in the Whiterun tundra, especially while it's raining or is cloudy, along with the occasional Celtic-themed music from the Skyrim Atmospheres track, my favourite. Then I absolutely love to get lost in the beautiful Rift; the more the forest is deep, the better.

That's for me & for now, though mostly resumes what I love out of the game.

Untold stories like people who camped out in the wilderness and got eaten by vampires. Not a single line of dialogue or text, but this kind of stuff. Bethesda really knows how to do this.

I agree with most of what you posted here.

I wear headphones while I play, and I enjoy the outdoor music, as well as the sound of wind, rain, water and etc. I love that when it's rainy or windy, it sounds just like as if I was standing outside during such weather. I also can never get enough of watching waterfalls. The flooded dungeons, and those with streams and waterfalls are my favorite. It says something for a game, where I sometimes just want to stop and admire the scenery.

It's the little things that really add to the immersion of the game, and I sometimes have to remind myself that I'm just playing a game and not really in Skyrim.

Btw...in all of my time playing Skyrim, my bunnies killed count has remained at 0. I only hunt the hostile animals.