If you enjoyed Morrowind then you will definitely enjoy this one! The story is engrossing, the character models are nearly photo-realistic (on a decent machine), and unlike many other RPG's Oblivion does not force you to "ride the main quest rail." You can go where you want, explore anything you find in your travels, pick flowers, enchant weapons (although the system as been extremely dumbed down from Morrowind's enchanting), create spells, and so much more.
I had only a few problems with the game. First, it is a graphics hog, so be sure your rig is top of the line. Second, while the auto-travel and the quest radar that have been added into the game are nice from an "ease of play" standpoint, they do kill some of the exploration and interrogation of the previous titles (thus making it feel less of an RPG at times). Be warned also, the main quest felt a little short to me, and although it would take you 40+ hours to complete every quest in the game, using auto-travel and quest radar significantly shortens gaming time.