If i had to compare DK:S with oblivion i would say DK:S is smaller with less freedom, but with a much more interesting story and with much better interesting / diferent stuff and much better sidequesting.
1st area is quite large, with a lot of stuff to explore (larian doesnt hold your hand saying where you need to go all the time). When you spend like 10-15 hours or so you have something (not spoiling) that radicaly changes your play and its like starting fresh with new cool stuff.
You never get lost in DK:S because the map is awesome, the areas are not so gigantic, but as son as you get to a landmark, you can bet there's something interesting there, and that will change your exploring goals
