Oblivion is great. I love that game. If you like rpgs i strongly recommend it to you if you can get a machine that can run it.
Some members who already have the game (that includes me :D) posted their first impressions here:
http://www.lucasforums.com/showthread.php?t=152586&page=3&pp=40) (starting at page 3 of the thread - note that the kotor forums are filled with rpg fans so keep this in mind when you read it ;) )
Btw, here are the system requirements:
Recommended:
3 Ghz Intel Pentium 4 or equivalent processor
1 GB System RAM
ATI X800 series, NVIDIA GeForce 6800 series, or higher video card
Minimum System Requirements:
Windows XP, Windows 2000, Windows XP 64-bit
512MB System RAM
2 Ghz Intel Pentium 4 or equivalent processor
128MB Direct3D compatible video card and DirectX 9.0 compatible driver;
8x DVD-ROM drive
4.6 GB free hard disk space
DirectX 9.0c (included)
DirectX 8.1 compatible sound card
Keyboard, Mouse
Supported Video Card Chipsets:
ATI X1300 - X1900 series
ATI x600 - x800 series (it seems that the x300 works too and some people are running it with the x200)
ATI Radeon 9500 series and up
NVIDIA GeForce 6200 series and higher
NVIDIA GeForce FX series
I have an x850xt and at high settings, I can say that this game draws a lot of juice from my GPU. The card runs about 15C higher than it does normally.