They kind of have, with the infernal machines and the new enchanting. It's basically what you could do with the cube, but more spread out.
I have been playing D3 for around a month now and I, sadly, have over 120 hours on my Demon Hunter, and breaking 60 hours on my monk. The expansion is a great breath of fresh air, but IMO overpriced.
Don't start a fire, you never know how many bridges you'll burn.