Skyrim looks almost lifelike with mods. There are a couple amazing mod collections on Steam Workshop for this. Couple mods I'd specifically recommend for immersion and atmosphere are:
HQ Texture Pack - Official Bethesda free DLC, improves textures pretty much everywhere.
Sounds of Skyrim - The Wilds/Dungeons, adds all kinds of new random sounds like animals and such.
Detailed Cities - Brings the cities more to life with plants and such
Lush Trees/Grass + HD Plants and Herbs + More Grass - Better tree/grass textures
That's Ice + Better Dynamic Snow - Ice looks better, snow looks better and forms drifts more realistically
Pure Waters + Kerplunk Watery Rocks + More Rain + Get Wet - Better water, better wet rocks, can get total downpours instead of just drizzles, and your characer gets wet in the rain
Alternate Sun Glare - Sun glare looks better
Enhanced Distant Terrain - Distant terrain looks better
Terrain Bump - Close-up terrain looks better
Spells Give Off Light - The fireball in your hands actually lights up your surroundings
Shadow Striping Fix - Big one, fixes the weird, buggy shadows on objects
Lanterns of Skyrim - Adds little lanterns to bridges and some other areas, adds some atmosphere
Dynamic Guard Helmets - Gives guards some variation in their helmets, or no helmets, randomly so they don't look like a clone army.
Cloaks of Skyrim - Just looks good, guards get them as well with the symbol of their city on the back.
Total performance hit for me was 5 FPS, tops, for all of them plus another ton of other stuff. Pretty negligible for the beauty it adds to the game. For me, the difference between my modded game and vanilla is like the difference between vanilla and Oblivion.