I had a proper go at this last night, and do you know what...it's actually really good now. They have made lots of changes. Loot of course, being a major one. In 3 hours I picked up 2 legendaries (decent ones too), and loot seems to have many new affixes that are quite cool.
The other major thing is difficulty level. We no longer have to run through the game 4 times to get to "inferno". Inferno, infact, no longer exists. Instead, before starting a game, you get to set the difficulty level (which you can do from the start). The higher levels provide much more experience and better loot. It's actually a really good system, because you can shift it around depending on how you are doing.
I am enjoying it so much that I am going to go and get the expansion