Open-world gameplay, craftable armor/weapons, potions, and enchanting.
Level-ups depend on skill use, not amount of enemies killed (though that can help with levelling up weapon skills.)
Fight dragons, giants. Take part in a civil war. Save the world. Shout your enemies to death (yes, really.)
Somewhat buggy. Avoid the PS3 version, to be safe. 360 Ok, PC best (as you can download player-made mods/fixes to the game.) Also can download the (watered-down) editor the devs used to make Skyrim if you're on PC and make your own mods.
Some guild questlines are worse than others. "New" features (to the series) poorly implemented (Marrage, dual-weilding.) Development is more to the casual gamer than hardcoe TES fans... which is ok, though some of us fans wished they weren't so keen on dumbing down a lot of features/equipment slots.