Oblivion is hands down one of the greatest achievments in video game history!!
What makes this game great however is the open ended gameplay, you could play for 50 hours and not even touch the main quest. Take how you felt for GTA 3 and times it by 100. You can do anything in this game. From making your own potions, buying your own homes, joining thieves guilds or becomin a murderer. Think of it and you can do it.
The graphics are great, on an HDTV you will be blown out of the water, even if you own a standard TV you will still be amazed. The first time you see Skingrad from the bridge is freaking amazing. While at first you might be overwhelmed you will soon find yourself in the flow of the game and be able to manever between play and menu's flawlessly. The hotkey function is excellent allowing you to equip items with one touch of the button instead of going menu hunting. If you can only affort 1 game in 07 make it Oblivion, you can't go wrong. You can spy, hunt, steal or just roam your way around a huge world.