Remeber Diablo 2, there are only 2 major differences! But it's still so good.
Update:
I've actually finished the thing in normal mode, and each of the 3 levels took 18 hrs to complete (roughly), or around 54 hours for the whole game. This is where I have explored every inch of every map. Though half-way through the game it kinda got really boring as it became "kill everything in sight" and the types of quest were simply either kill or retrieve something. Don't know how long it will take to finish the epic or legendary modes as for me, these kinds of games are "once around the bend" only, as there will be nothing new.
The value of this thing really only goes up when you have friends to play with all the time. The single player is simply too lonely and monotonous.