Simply put, probably the best game in the series. FPS and RPG fans unite, this is just the game to bring us together.
The high points of the game range from delving deep into unexplored caverns, or joining the guild of your choice to complete a wide array of side missions, helping out local townspeople, or even doing the main quest. When you get bored with one character, you start another and play a completely different way, changing the game experience all but entirely.
Another plus of this game is the wide variety of mods that exist for it. If the game in and of itself does not fit your playing style, then you can throw a few add ons at it and remake the game to your liking. All of this through the convenient modding apparatus attached to the game launcher provided by Bethsoft.
That being said, there were a few downfalls. In its time, the game was a system hog. Anything running in the background would drop your FPS like a rock. Also, there is something to be said about the "innovative" AI that gets stuck behind rocks and you can kill them with arrows, or the NPC that chooses not to follow its set path and you spend hours searching through the wilderness just to turn in a quest. All in all, Oblivion was a very solid game and I personally spent a great many hours delving into the realms, and by this point you could probably find it in a local bargain bin, and it's definitely at least worth that.