The new cosmology consists of:
The Astral Sea - Contains the homes of the gods including Hell.
The Elemental Chaos - All the old elemental planes (earth, air, fire, etc) all 'smooshed' together.
The Abyss - Home of demons, located at the 'bottom' of the Elemental Chaos.
The Feywild - Celtic Otherworld, close to the world adventurers live in.
The Shadowfell - Place of death, evil, scary. Like The Feywild, also close.
The Far Realm - Where Azathoth lives.
I prefer the Astral Sea to the old Great Wheel. Thor doesn't have to live on Mount Olympus now and it isn't tied to the nine alignment system, which I think is inferior to three alignments or none at all.
I like the Feywild a lot, it's got a very Celtic mythical/folkloric feel. You can even find Fomorians there. Shadowfell and Far Realm I'm meh about, though I think including the Far Realm is a good idea as people love Cthulhoid monstrosities.
The Elemental Chaos is a bit weird. The concept is tied to the elementals in the MM as they have also been 'smooshed' together. Probably not a good idea tbh, but at least they're trying to do something a bit different, which counts for a lot in my book.
My ideal set up would be to combine demons and devils into one race. If anything the division has now been emphasised. Devils are still lawful, demons are now much more chaotic. 4e demons are destructive forces of entropy a la BECMI. Although this isn't how I would've done it, it is a cool idea, definitely superior to the old demons.