This is a proof-of-concept, not a game
Technologically, Oblivion is stunning. After escaping the initial dungeon, you emerge onto the sunlit surface of a vast wilderness. The first thing I did was hike up the nearest mountain and try to explore into the deep wilderness. Oops! No deep wilderness, you cannot travel this direction any more. Oh well, wander around and explore the world. Nothing memorable to encounter, just generic enemies and generic dungeons.
The game is fantastic to look at, and it's exciting to see what will be done in future RPGs with the graphical features displayed in Oblivion, but as a game Oblivion is soulless and devoid of anything cool or heartwarming.
Well, the fact that it's not really a game, it's an engine with a few half-baked RPG elements thrown in so consumers can rationalize why they just spent $70 on a terrain-modeller.
Oh yes, the SpeedTrees look good from a distance, but a cursory look reveals that each tree looks identical no matter what horizontal angle you look at it from. Trees in Oblivion are little more than glorified sprites -- not that I have anything against sprites and 2D graphics.
The Bottom Line
A waste of time and money. In the next few years we will probably see an engine like Oblivion's put to good use. People need to look back and remember what made classic RPGs great -- Drakkhen, Baldur's Gate, Betrayal at Krondor, Ultima VII -- before anything truly special can be added to this nearly-dead genre.