This is perhaps my most immediate impression aside from the 17 fps on a gtx 1080(naturally alpha)  and the common bugs already submitted for review by the community.

When I ask myself "what is the most crucial aspect of diablo esque action rpg combat?"  One thing springs to mind:

"It has to be fun enough to carry the game!"

Now mainly this is because the VAST majority of the game will consist of your character using a set of certain abilities  to dispatch hordes upon hordes of enemies, and that action has to "click", which is a far cry from the current system:

Combat speed:  

It's painstakingly slow... the animations of pretty much everything combat related are acting out as if they are done under water.

Lack of tactile feedback  from melee: 

 Swinging be it a thunder hammer, chainsword, or a power sword leads no no feeling of "oomh" from some of the most viscious melee weapons in fiction.  I'm not swinging a thunder hammer here, i'm swinging a "stat stick #325664"

and it does huge disservice to the visceral melee combat in warhammer 40k.

A wide arsenal of pea shooters:

Ranged weapons in general not only lack any tactile feedback, but also feel  toyish.  The plasma shots look  impotent and very much so not fun to shoot.  The auto gun has a weak monotonous thud that grows iresome five minutes into the game.  The cyclone missle launcher shoots what appears to be chineese new years firecrackers to a staggering range of five meters.  The melta gun is perhaps the most unenjoyable ranged weapon i'm yet to use in an action rpg.   The glowing  ray of measly damage  is just mind numbing in how utterly boring it is. You just  glow mark this enemy and his health goes down untill his ragdoll falls over with complete lack of weapon feedback.

All ranged weapon abilities feel exactly the same:

The difference between those is almost non existant.    I fail to memorize their key presses just because of how utterly the same they all look and play out.

 "Oh, this shoots in a bit different rhythm and has 7 more dps"

"this melta beam looks and acts the same as the other melta beam but does 3 more dps"

"so this burst fires and other auto fires?  they all mow down the mobs the same way so who cares?  let me just mash one button the whole game, they all the same anyways"

I'm sorry, but the way the combat plays out currently, I just don't feel like exploring the game.