So after bumrushing to 77 I think I can share some thoughts on 3.1/abyss:
The new atlas mechanics are awesome, the new rares seem to be pretty scarce though, I got only 1 shaper rare out of 4 maps I could run so far. I'm sure people will have it down to science soon enough though, but until then you have this beautiful sense of wonder and exploration. The abyss mechanic is nice, but honestly when there's like 3-4 in a map, it starts to feel like a chore, especially once they go to 4 holes or spawn the mini dungeon. And then you run into a breach which is done in a minute including looting ... The new abyss items are nice, but all of them have the breach ring syndrome - so much random shit that I'm not entirely sure is necessarily better than the items previously. Sure, once you have all the resists and look to squeeze the last bit of dps from your gear, they will come in handy, but defensive stats are simply more useful when you start hitting maps. With the amount of slots available these days, the one jewel that comes with the belt is like a piss in the ocean. Then again, I'm playing scorching ray, so flat damage is kinda useless to me.
The new maps are absolutely gorgeous, I think my favorite ones that I ran so far are City square and Haunted mansion. The lack of harbinger orbs is sad, but I guess they want you to trade a bit, otherwise 3.1 rocks !
This is probably the first time no part of the game feels unpolished or lacking. Sure they could add voiceovers to a5-10 and so on, but otherwise everything feels fleshed out.