I got a guest past off my brother, and finished up to where that allows you to play up to pretty easily. Imo it definitely wasn't as good as Diablo 2 was back in the day, i.e. I'm not going to go out and buy it or anything. It had a real WoW feel about it, just the way the towns were set-up and stuff, and I didn't like it how it pretty much held your hand as you went through the start of the game, telling you exactly how to do every quest (I'm not sure if that continues later on). I liked Diablo 2 because while it had a strong storyline, it still allowed you to go off on your own with most areas being open, unlike D3 where you seem to pretty much just be following a path the whole time (at least at the start I was). Don't get me wrong I still though it was a good game and I enjoyed my few hours or so playing it, but I it didn't live up to as good as I thought it would be.
@ puddleduck - You can still play easily play single player, you just don't make your game public. Although I think you still need to have an internet connection. I played the first part myself.