-Being able to blow out candles and torches aswell as light them would be brilliant. Getting in a dungeon that is pitch black would be awesome then lighting all fire sources! Camp fires and all other flame sources should be interactive also.
-Slippery ice and rocks on slopes and stronger water currents that put you in ragdoll down untill you can compose yourself.
-Locational damage, bleeding actually is visible leaving blood trails. wounded will cower ask for mercy and mean it, if you heal them you can have them as an extra companion. thiefs can sneak up on you and steal from you.. and assassins can attempt stealth kills on you even when your in dialog haha!

-foot prints
-Bees will freak out and 100's will sting if the nest is bothered.
-Fish that can swallow you whole

-whales, and an ocean and islands to explore with the boat mods.
-people for the most part panic and run from dragons and hide. Dragons will hunt you on the ground when they can't see you in the woods and what have you. Dragons will mess with you, tease and play with thier prey not always killing you. leaving you to feel like hiding while they sniff you out.
-Most Predators should have a hunt mode trying to look for you where they last saw you and don't give up so easily, they are hungry slowly staking listening for any noise. So don't step on that *snap* Oh crap!