So far everything looks pretty, flashy, and otherwise well polished. Sure there are quirks that come up going from 480 to 1080+ resolutions, and those are being addressed as they roll through their list of changes. All in all, Im very happy with the updated graphics :).
The one change that, to me, makes the spells feel underwhelming now is the lack of light given by the lightning spells. I honestly feel like they need more visual noise. Lightning sorceress’ didn’t just have Lightning beams of death in their arsenal, it was quite powerful and fun to use their starting skill Charged Bolt to blast waves and waves of blinding, squiggly white deathballs skittering across the screen. The current preview in the Blood Raven graveyard has the sorceress using this and it feels… small. I personally think its the lack of visual noise behind the spell. Again, just my opinion on the matter 
Cant wait to play this, test this, anything i can really 
fingers crossed heres hoping.
What? NO!
Please don’t brighten the game. I’d prefer less flashes. The fire explosions are already too WoW like.
The skills work exactly the same. The lightning now just actually looks realistic and less like giant white lines of c*ke flying around the screen. Once you’re spamming chain lightning or charged bolt with 22 bolts, there will be PLENTY of “flashing” going on. We don’t want this game to look anymore like D3 or WoW than it absolutely has to.
There is no transition from 480p to 4k in D2R.
Diablo II Resurrected uses an entirely new 3D Engine which uses physically based rendering, which is the reason for the nice shadow and light effects etc.
This 3D Engine rests on top of the sprite-based game.
The background is still pre-rendered I believe, and only light-effects are dynamic and because of physically based rendering, the surfaces of those pre-rendered backgrounds react to dynamic lighting. Its a cool way to remaster D2, because it allows for the actual D2 game to be untouched underneath.
As for the darker looks of D2R vs D2, I love it. IMO some areas look even creepier and better than the original could ever achieve back in the day with the tech at the time.
Light-Radius works very well in D2R and creates really great visuals with the new 3D-Light-Tech used.
I always found the Blessed Hammer skill lacked punch. If they could put some sparkles or a rainbow particle effect on them it would really elevate the visuals, especially since we will be seeing it a lot. Just think how great all those sparkly colorful spirals of death would look in the grim darkness of the Chaos Sanctuary.
If there is one thing this game DOESN’T need, it is more love given to Hammerdins.