Fable 2 is awesome! It's one of the 360 games i played the most, and soon Fable 3 is here. I recommend you to buy Fable 2, its well worth the money, and you will have alot of gaming hour in front of you.
Comparing Fable 2 with Oblivion isn't fair. There is some thing that are the same, but the feeling in the whole atmosphere is much better in Fable 2.
