The Elder Scrolls V: Skyrim apparently will be completely eschewing classes, whether premade or user-generated.
Leveling up will allow the gamer what abilities they want to employ at that particular time.. An example given is that a stealth character can choose when they level up to wield two-handed axes. The character will remain stealthy - but have the ability to swing a massive two-handed axe.
Another combat feature is the ability to dual wield. Players can dual wield not only weaponry but spells as well, so a player can have an ice spell in one hand and a force spell in the other. Freeze them, then slam them with a telekinetic slap.
As far as enemy scaling, Bethesda states that it won't be as drastic as it was in Oblivion, and more like Fallout 3.