Here's what I noticed from the streams:
1) You cannot stop and tank anymore. No more Gloom nor snapshot of it.
I was watching a RF DH playing on stream and he was literally being raped by any monsters which don't die within a couple of hits. Saw a REFLECT pack and knew it was the end for him. Had to revive like 10+ times before he finally killed it. Then he went for one of the major Act 5 boss and was raped again. He retried at least 10 times before giving up. RIP RF.
2) It's back to pre nerf Inferno again! DH's have to constantly move, then hit, then move. If you miss a step and stop, RIP.
Currently watching Athene on his DH on Master difficulty, and he is dying plenty too, not as much as the previous DH from 1) though. He isn't killing the mobs, just running past them to try and skip them. He is using L4N which is useless IMO, the discipline regeneration is not enough, low stats, low armor. I've seen some of the new gear and they add tons of high stats (300+, high armor). I must add he is really bad at controlling DH, probably spend too much time on poe aka piece of !@#$.
Seems like slow/freeze/charm enemies and life regeneration will be extremely useful in RoS,
3) Group play is really important now.
If you want to clear the game efficiently, you need a good team of melee and range. Those who do crypt runs will get a good idea. Different roles contribute different advantages. A really good zdps monk will do wonders for a DH or range char. A high damage decent EDPS DH will make clearing the mobs so much faster.