I've only player a few hrs, but the atmosphere is really immersive, I love how the game is fully 3D Vision enabled out of the box, the vistas are breathtaking, even though the character animation system is still a little quirky, but I've been spoiled by BF3's character animation.
I feel the world is more carefully crafted than Oblivion's and I love how cities are now open, and load times are almost nil, enhancing the sense of immersion, the soundtrack is moving and the transition from one theme to another is almost seamless as far as I've seen, making you feel the BGM has composed as one never ending piece of symphonic rapture.
I also like how quests are more organic and don't interfere with the flow of your experience.
The game is not without its faults, but nothing I would consider to be a deal breaker, I was also surprised by the changes to the UI and some control issues mentioned before like the counterintuitive inverted mouse buttons (same as with Oblivion) but that's the way it was with Oblivion when I played it after playing Morrowind, and I think the changes are beneficial in the long run.
Many times I've been talking with an NPC only to watch him dissapear and appear sitting on a chair behind me, the character animation is a little quirky but is far cry from Oblivion's or Fallout's android like animation, but these are just minor things that don't break the game. The game is super stable out of the box, unlike Oblivion on release with its infamous constant CTDs, but that may change once I start user created content.
And that's just another plus, I can hardly wait for moders to start pouring their creations, to me that's what made Oblivion such an engrossing experience, and I am salivating at the prospect of enhancing Skyrim's experience even more
That game is a pure PC killa!! 
