When I started playing Oblivion, I was very impressed. The music was amazing, the graphics awesome and the gameplay filled. Oblivion certainly give a very good impression to someone who never played it before.
Oblivion's gameplay is very good, filled, in a way that will prevent you from getting bored. Using the fast travel feature to travel where you want ruins a big part of the game, as you will never get to see the beautiful landscape, creatures, caves, mines, forts, e.t.c.
The combat system is simple, but that doesn't mean it is bad. It is very realistic, with staggerings, knockdowns, power attacks, fatigue, e.t.c.
Magic is an important part of the game. You'll miss many things if you ignore magic. Mage characters also have a very easy time surviving at lower levels.
The graphics of the game are just beautiful. No need to say anything more.
The music is awesome. It fits perfectly with your current situation, changing when in combat, exploration, e.t.c. It is a pleasure listening these songs.
Now, about realism. The player should try to roleplay with as much realism is possible, cause it makes the game much funnier.
The AI is hugely improved from Morrowind, but it still has many big gaps.
Generally, Oblivion is awesome. If you are bored, it certainly will satisfy you. If you don't have it, go and buy it! It is more than worth the money.