This game hypnotized me for awhile!
When you start the game, you're immediated asked to choose your race/gender. Instead of picking from preset faces, you start with one face per race/gender, and an intimidating amount of slide bars. For human-ish characters, it's amazing how so many tiny little changes will result in an amazingly different looking character. For Kajiits and Argonians however, there aren't too many striking changes in your character's appearence.
If you liked Morrowind, you'll most likely enjoy this game. There are some changes besides the ones you're probably already aware of (graphical and combat system improvements). Bethesda narrowed some of the skills down. What do I mean by this? In morrowind, there were Light, Medium and Heavy weight armers, while in Oblivion, it's just catagorized in Light and Heavy. It's the same with the weapons. This makes the game more accessable, which may appeal to some, but not too much for the ultimate rpg person.
One of my major concerns with this game was the lack of variety with ruins and small dungeons. Most ruins are just generic caves with goblins, rats, or bandits in them. They are very well done, but I really miss Dwarven ruins, Daedric ruins, and the other varieties. Oblivion gates sort-of fill this gap, but 9 times out of 10 they come off as annoying road-blocks.
There are also fewer unique items. There are enchanted items, but nothing too out of the ordinary. In morrowind, there were rare, hard to find variations of armor that actually looked different. I kind-of miss that.
The biggest problem I've found however, is that the world changes with your character. As you level up, the world levels up. The guards are constantly at a higher level than you are, enemies get harder as you get stronger, so there's no real incentive to level up or work on any of your skills other than unlocking better armors etc. For examle, you level up, and wolves are replaced by timber wolves, which are stronger, so you never really feel powerful as you get stronger, unless you're fighting rats.
All in all though, it's a good game, and a "must buy" for RPG fans.