By far this is my favourite game to play, over and over again.  I think I am love with the Elder Scrolls' world, but that is besides the point.  There are many nice improvements that the current game released by Bethesda has over the previous games, Morrowind and Daggerfall.

Like its' predecessors, Oblivion has hours of game play and variety for the player.  Unless you have oodles of time, you can always keep yourself busy with quests from the guilds, daedra deities and town inhabitants.  What is nice is that guild quests have wonderfully, fleshed out plot lines.   If fighting is more of your type, there is also plenty of ruins and abandoned forts to go around and gain experience.