You got it ! that sounds awesome, some ladybug like creatures, or toads in the water..sit by the water and read a good book while fishing...

General junk you can pick up, also nice if you can put it down again without wreaking havoc.

Candles, lanterns, bug lamps all light sources and like the junk must be pick and place.

Notes.
I'm a big fan of notes that tell a little story. Remember the abandoned shipwreck to the north in Mw? Open a chest, pillows. Open another chest, pillows. Look in the corner, piles of pillows, lol. Looking around you find a note, an invoice in fact, the entire ship load of 40 pillows was destined for Drarayne Thelas in Balmora. How I laughed, such a tiny detail. Then you find it's actually a quest with an awesome reward of the unique extra-comfy pillow: "Your sleep is very restful on your Extra-Comfy Pillow" appears every time you sleep. This is what I call detail, I also take it as a sign that the devs were having fun and fun is contagious

I'd also love to have multiple carryable light sources again, per Morrowind. Lanterns, candles, all of that good stuff: why were they bolted down to the tables in Oblivion? My favorite thing about Morrowind was being able to pick up virtually everything but the furniture.

A more living world as mentioned already. In oblivion there was a weird lack of travelling merchants, children, dogs, wild horses, birds, non violent fish.

No Omniscient Guards. I know it seemed like such a small thing, but it actully ruined my criminal experiences in Oblvion.

Also being able to walk on rooves. In Bravil and Leyawiin it was very possible because tehy had flat rooves adn stairs leading there. Also it was possible in Bruma, but for some reason you ended up getting stuck alot, it was annoying.

I completely agree with more atmospheric birds, insects and fish. Fallout New Vegas actually did a decent job with underwater fish and plants.

Considering the experience Bethesda is getting with flying animations due to the dragons, I think they could do a great job putting birds in. Red Dead Redemption did an excellent job with them, so I'd love to see Skyrim feature them, even in a non-huntable form.

Insects are very rarely implemented in open-world games, which is a shame because they're majorly atmospheric. Seeing butterflies flutter around fields, scorpions skittering along cave floors, and nests of wasps hanging in forests would be amazing. MGS3: Snake Eater did a fantastic job wit this. I'm not entirely sure how insects would cope with Skyrim's frosty environment, but I know the whole region isn't extremely cold.

Ive seen Butterflies in Oblivion.

Unless the animations are REALLY credible, I'd rather let my imagination do the work.

" Being able to see your own feet. "

And it would be cool if you can shoot your feet with a bow!

Clouds cast shadows, visible breath in certain atmospheric conditions, footprints in snow, have armour and clothing make slight and appropriate noises (rustling, creaking etc) which affects sneaking. Water splashes. Steam above hot food and cooking pots.

1st person sitting and sleeping.

In Oblivion, when you did a roll in 1st person, the camera staid upright. Would like to see a quick flip in the viewpoint. Maybe wouldn't spam the movement so much if it caused actual visual disorientation.

Be able to move things in houses easier.

Use a staff with 1 hand (since a Lich could do it in Oblivion but I couldn't, also b/c it looks terrible with 2 hands).

Hell yeah. Never really figured out why they changed this, it took away much of the fun in trapping souls. Gems became mere batteries for recharging your weapons, rather than trophies of battles won.

Allow you to enter a building through windows. This is a must have for thief, assassin characters!

Open air markets, celebrations, merchandise transport caravans that can be attacked on the roads, people playing instruments, saddle bags, real time ladders.

Insect life,birds,travelling merchants, bonfires,general beautiful scenery...

I will bring up a few subtle details that I think the Elder Scrolls franchise has been doing in the last few installments, and then some I would like to see.

• Clutter Items. When you go into somebody's house you see plates, food stuffs, dining table and chairs, bedrooms with clothing in them. It is not something that you might notice consciously, but that is kind of the point. Your brain is well suspended in the belief of the world of Nirn and has no good reason yet to exit and let you know something is amiss.
  
  
• Believable Item Rarity. This one is from Morrowind with their static items and goes hand in hand with the less valuable "Clutter Items". I loved the rarity of Daedric items and even items like Glass and Ebony. It really struck a proper balance, and I still remember my first play through the game and discovering the different armor pieces, I really felt like they did that well. It was a subtle thing, but the rarity of the items and where they occurred just made sense (still remember finding my first glass armor at Ghost Gate and my mind just believed that "this is where I would find something rare, at the garrison outside the Ghost Gate." It just seemed to make sense).
  
  
• Natural Walking Speed. This subtle detail I will take from Red Dead Redemption where your character actually looks like he is walking at a natural speed, and in a natural way. They did this very well and it really added to the immersion.
  
  
• Natural Salutations. Again with RDR, a natural "salute" or the way people said hello. It wasn't overbearing (like it has been in some games), and it felt natural. A subtle detail that goes a long way when added up with other things. And to add to this subtlety a lack of salute, maybe just a quick glance instead of a verbal exchange would be more natural in some cases. Make my character feel less like the center of the universe (if you've seen Inception that can be a good comparison, you don't want everybody around you to "stare" or continue to acknowledge you're the only living person in the game).

People with different bodytypes - fat people, skinny people, medium people, really muscular or really wimpy looking characters. It would add to the variety of characters that would be possible, both as NPCs and Player Characters. I previously mentioned the wish to have a pale emaciated high-elf necromancer with a bony chest, but at the same time I could also create a really obese Khajiit and name him "Fat Cat", or a very muscular Bosmer with a bad temper named "Disapproving fan"

I must agree with you here. It is subtle because I can play through Morrowind and Oblivion without thinking about it much, but once you start to notice it can definitely break immersion.

There was a mod for Oblivion (The Deserts of Elsweyr) where some of the population had different body frames (some fat) and I thought to myself that is really something missing from the vanilla game.

However, I would like to point out they are now going add decals, tattoos and scars for variety so they are definitely taking direction to make characters more unique.

The biggest source of feel and immersion for me in Morrowind was all the clutter items. They really fit into the world and gave it a culture, it was amazing throughout the game. From the census room in the beginning to shops and ashlander camps.

Chips and marks left on armor and weapons after a very tough fight.

like seven dragons said.
I want natural walking like they did in red dead.

Able to see my own feet.

Able to see my own jackolantern(s).