So I just wanted to share some things I think would make the game better, with the upcoming expansion in a year or so (hopefully)...
First of all, I've gathered four classes, 2 from D2, and 2 from the warcraft universe that I believe combined, could make for a class that D3 is lacking right now, and they are : druid, necromancer, beastmaster and worlock. I know it looks like much, but bear with with me. This combination can take the best from all 4 classes and make something better, something no RPG has seen before; we have a corrupted nephalem from what the ending for RoS suggests, so why not a half demon type possessed nephalem, with the demonic side being a kind of beast, similar to Grigor from PoE, but not quite.
The class can have a tab dedicated to curses, much like the necromancer from D2, a beast summon tab, but the catch is that you can only summon from corpses, like the necro, with passives that go along with each build the class can use, like for example a summon resist passive for the minions.
Also, from the D2 druid, this class can have shapeshifting, into a wolf or bear, with passives for each of them.
So basically, you can go with a beats melle class and use shapeshift, or a ranged build with minions and curses, or, a demonic hybrid build, that takes from both.
This class would introduce a new damage type (demonic damage, much like what diablo used in act 4), and as inspiration for the class mechanics and art, blizz can look at Ilidan, for an emolation type skill, and the way he transformes in W3.
From the warcraft druid, a good skill this class might have is the ability to summon treants from treas.
As a final idea for this class, it would be nice if he/she had a passive that allowed the swapping of weapons, for example melle weapons for the shapeshifter build, and ranged for pet build.
But that's enough from my class ideas for now.
About the new act, in my opinion, act 6 should at least partially be in the Skavos islands, because beach and jungle levels are loved by us gamers, see games like the Risen, Gothic, Dungeon Siege, and Sacred series, PoE, all of them featured jungle/beach maps, and where well received.
A cool thing would be to turn all the water from all the act black or red, for one month after the expansion comes out, like a visual reminder that it's launch month.
I've studied a lot of the artwork that came out for D3, and one of them featured a panoramic view of Skavos, with a giant waterfall, that can serve as a transition point between zones, much like the fall in the cathedral from act 1.
Monster wise, I loved the treant like mobs from act 3 in D2, and the montain giant from W3, Skavos being a rocky-ish so it would go well. I'd love the return of creatures from D2, such as the blunderbore, overseer, bloodlord, even the concept for a creature called reziarfg, even if it was just an april fools joke, would go well.
For a boss before the final fight, my nominee would the Na-Krul, one of Diablos strongest allies back in the days of D1.
Story wise for act 6, parts of Tathamet still lie somewhere under the waters of Skavos, Diablo sets out to become even more powerful, possesses a giant sea creature, which can be the first boss, but the creature is only a distraction for the nephalem until he finds what he seeks, then you beat Na-Krul after some plot twists, get to Diablo, beat him, he comes back to live and the nephalem realizes that the only way to stop him is to contain him, this way we can go back to the Tal Rasha part of D2, and just before he/she becomes full deamon, the aspect of Anu comes forth through Imperius and helps contain the evil that is Diablo, saving the world, but killing the angelic side of Imperius in the process. Tyrael keeps helping you, in the end he becomes the new leader of heaven, Imperius is looked away in pandemonium, leaving room for a D4 storyline, and we can have a happy ending
Now a few ideas regarding the general game...we need more colors for portals, like when you teleport in campaign it should have the original color, but when you are in adventure more a different color, when teleporting from a rift another one, and when teleporting from a greater rift, you guest it, another color, this is just esthetic, but it makes a big difference if you like the little things in a game to matter.
Also, i strongly think D3 needs a new socketing system, the current one is to dull. Being a D2 player also, I consider almost all socket numbers need to be raised, 3 for helms, 6 for chest armors, 6 for shileds, 3 for 1h weapons and 6 for 2h weapons, and 4 for pants. And if they change the socketing system, runes and rune words MUST make a comeback, so we can have something more to socket then just gems, also if sapphires would make their way back to the game it would be great
That's all the ideas I have to share for now, if I'll get a good reception on these, I will be back with more, maybe even a full class/ act sheet complete with skills, passives, maps, mobs, etc.
classwise, we already have curses, we have pets and those are in what we now know as ''witch doctor'', and we have a ''half demon'' class which is dh
sure we dont have shapeshifting (actually we kinda do... beserker, vengance and souch fill that gap) but i cant really see what the new class can be...
also your story line kinda lacks... the wow factor.... its all so expectable, there are no real plot twists.
sure we know diablo is free, we know he can posess anybody at any time, we know he will come back... i would be kinda ingtrigued to see Na-Krul (even tho i didnt play d1) cause he seems cool and powerful. i would love to see somebody absorbing diablo in himself but controling him like malthael did, but in a different way
first boss is some sea creature (kraken/chutlu/gyrardos-like monster), second boss is Na-Krul in his regular form, but we dont kill him, we simply weaken him and his minions come for us
third boss is a mountain giant that contains something we need to reach Na-Krul in his lair where he regenerates after fighting us and we catch him off guard
Act boss is Na-Krul, but the fight happens in phases
phase 1, still injured Na-Krul, a short fight filled with lots of his minions
phase 2, he runs away to find a way to deal with you, he summons 3 mountain giants to distract you, each in a diffferent area (beach, mountain bottom, mountain pinnacle), each with some kind of different fighting style
phase 3, we go through army of demons and fiends, not like stonefort where there is an army of demons but scattered widely, but literally a cluster of minions without any space in between
phase 4, Na-Krul absorbs diablo, changing his form and powers, and that fight is also split into a few stages, one where takes us to terror realm (diffferent than the one from diablo fight) and one where he enrages and does something awesome and fearsome to make us shiver with excitement
we defeat him, imperius thanks us, he realises he is the only one to contain the spirit of diablo, he absorbs it, he turns demonic, and the other members of the angiris council lock him in the pandemonium fortress or the place we first found tyrael in act 2 of diablo 2
I was also wondering about next expansion (as they from the beginning told about two).
On polish site I predicted crusader, but not by the name (I call it just knight).
As for further expansion - I don't think that any classes will be demonic / angelic - Blizz told before that Nephalem is more powerful than both of them. And what is more, Na-Krul wasn't Blizzard product, but Sierra if I remember correctly.
I'm also thinking that we will get some kind of shapeshifter, and after Skovos has been mentioned - I suspect some amazon/druid hybrid, using javelins and other light weapons. (ps. sorry for my english, must polish it :P).