If you liked the Morrowind series, you're going to love Oblivion. Again the folks at Bethesda have produced a quality single player game that is so ingrossing, that you will totally forget about the time, where you are, or that your mate is telling you it's 7am and you need to get ready for work!
First, a few of the things that you will like...
Graphics:
Best so far of any in the series. Even on low end machines, the lighting and shadow effects lend to the believable reality provided by the engine. The vast variety of trees and grass sway, you can easily see the mountains in the distance, and even the sky looks and feels... "right". Yes, details pop into view as you move along, but with some minor tweeking of the texture size and view distance, this is soon forgotten. And unlike other games in the series or expansions, you will not find large barren stretches of land devoid of life. You will see small villages, homesteads, ruins, caves, and creatures of all varieties. If you have this game, stop on a hillside and just look around, and you will see what I mean. I would want to live here.
Sound:
From the clomps of the horses walking past, to the swaying geass, the creak of a door, or the birds in the trees, the sound in Oblivion is top notch. All most all dialog is voice acted. All actions have sound that is perfectly matchs with its action. Ambience and audio color paint a living world that you are moving through. Even the tombs and underground areas have the proper amount of echo and feel.
Interface:
While usable and uncluttered, it does get a bit unweildy at times. You can easily setup hot keys to equip weapons or cast potions, but are limited in the number you can setup. Getting to the ingame map is more difficult than necessary. Also, you mouse users. Don't expect to be able to map common actions to the mouse buttons from the games interface. They are already map and cannot be changed that I have been able to find. They are mapped in an intuitive manner, and so far not posed any real issues.
Avatar:
It seems that Bethesda just can't make the adjustment interface for your avatar have a truly representative face like you will actually see ingame. Your results in game will look much better than what you think it will. This time, they have allowed many more options than ever before. Only the face can be adjusted after you pick your race and gender. My suggestion would be to use the random face feature to get something close to what you want, then fine tune from there.
Conclusion:
I have actually worried about Oblivion taking long term players away from Horizons, ( even if for just a month or two ) if it was done as well as it looked. My fears stand. Those that get involved with Oblivion will be drawn in to a very vibrant world full of exploration and intrigue. Don't be suprised if a few of your guildies and friend disappear for a bit while they play this, because it, like Horizons, is very involved.
A guildie of mine mentioned it would be a good game to play on patch day. "The shards are back up? ( 2 hours later ) Ok, just a minute..."