Howdy!
First off, this game is simply amazing and have incredible potential to be a real Diablo/PoE slayer! Well done!
I am a gamer who started out annihilating demons in Diablo 1 back in the days, have been playing a crap ton of Diablo 2, Diablo 3, PoE and Grim Dawn so I see myself as well trained in the art of playing ARPGs.
With this said, i have some feedback based on my time with Wolcen so far since release (I bought it way back in early release and played the beta a lot too).
Here goes, with no particular order of importance.

Stats/Information visibility
Edit: I felt this needed a separate section to be clearer.
1) Everywhere were there is a text stating something along the line of "Increases damage", "Reduced range" or whatever, we want to know the values of these. One example is where you select modifiers on an active skill, the attributes listed to the right doesn't reflect any modifications.
2) As pointed out further down this thread some skills have information that doesn't really seem correct, weapon skills claiming 0m range for example, this should be corrected and any additional information about a skill should be listed as well.
3) We are currently missing/have low visibility on information about cooldowns, buffs, debuffs, pets etc, this is very needed.
4) It would be nice when hovering an item to be able to see more in depth information on them, for example if it has 30 critical chance rating, how much added crit chance does that equal to? (could be a modifier like alt key to see more info)

HUD/Settings
1) The lack of a keyboard bindings is frustrating, we need to be able to set the keys we want to use ourselves.
2) It would be very useful to have "item filters" as in PoE so you can for example filter out any white/blue items that drop and only see the higher quality stuff.
3) I find myself spamming "alt" key alot to show items on the ground, would be nice if we could "force show" items on ground at all times, maybe have alt as a toggle instead.
4) Edit(Added): I would like to have energy shield separated from health bar, when enabling the option to show numbers it looks kinda bad.

Difficulty
Please please please, do not listen to those complaining about the game being too hard, the difficulty is just perfect and refreshing from a world of casual gameplay, I had an amazing fight with the 3rd boss on a fully modded expedition at my current highest available veteran rank, i was actually sweating when it was over! (Unfortunately the game crashed on me just as i went back to town...).
If you must cater for those more casual players, have an optional lower difficulty setting or something.

Offline/Online
I love the ability to play offline, have been requesting this since the days of D2. A small change you could do is remember what we played and launch directly to offline mode if needed (mostly annoying now that the servers are down when we have to sit through a "connecting..." dialog before being able to play)

Active skills
1) As i seen some others point out, some skills are simply too weak or just have no real point over another.
2) I would love to see some more crowd control skills like fear/stun etc.
3) Some more interesting modifiers could also be added that would change how a skill is played out, you have made some good examples of that already (like +1 zombies, auto-aim for turret etc), I just want more (greedy i know).

Passive skills
I really have no complaints here, I'm sure the wheels will be tweaked/nerfed/buffed/changed as we go, but the concept as a whole is really great!

Potions
Having only 2 potion slots feel a bit too little, I would love to have lets say 2 health potions and 2-3 utility potions, i understand if you don't want to allow 5 health potions as that would completely destroy the difficulty you are aiming for, but maybe have fixed slots for different types of potions or something?

Main stats
I would love if these were a bit more meaningful, for example if toughness also added armor/material resistance, agility added dodge/movement speed/extra stamina points, wisdom added elemental resistance, extra willpower/rage, etc.
Currently all our extra damage comes from our highest main stat which basically makes toughness the best choice since that gives us the only defensive stat available amongst the main stats but still gives the same amount of damage as the rest.

Endgame
Having just reached level 51 and completed a few expeditions and city building tasks I just love this endgame, its still a grind but with some added meaning to it, would love to see it developed further but currently I have no complaints or additions to ask for!

Crafting
I have collected quite a few of the crafting materials but have not yet found a use for them, I would love if in addition to this system we had a more traditional system where we could craft our own armors/weapons from scrapped loot for example, allow us to dismantle leather armors for leather resources, steel weapons for steel, bows for wood etc. Maybe have crafting patterns drop as loot as well. You know, standard stuff :)

Gems
This might be related to my build as a crit based summoner/ranger hybrid but i really have no need for any of the support gems except for the "crit chance" one, there should be a way to mix them up a bit instead of having "life leech from X damage" on every single one for example.

Apocalyptic Form
I'm not really sure about the current state of these. I usually use them as a "holy shit" button, when I'm out of potions and about to die. I'm not really a fan of them making us immortal, also currently I make a lot less damage in apocalyptic form than i do in my normal form. I would however not like it if I'm immortal AND doing a shit ton of damage so I'm not sure how to solve it, maybe have different apocalyptic forms buff different stats instead and allow us to continue using our own skills, for example, one apocalyptic form could be a "tank" one, increasing health and resistance by 200%, one being the agile one would increase our movement speed by 100%, unlimited stamina points, 50% added damage etc.

Items
1) I don't have very many complaints here really, I would like to see larger diversity on stats though, for example I have never seen a catalyst drop with anything "attack" related, its always "spell" related. Having "attack" stats on a catalyst would further help me in my hybrid build for example.
2) I would also love to see more types of stats overall.
3) This may be since I haven't played a lot yet but so far I haven't seen any "build enabling" stats, like "adds +1 projectile", "curses on hit", "allow skill X to be used with melee weapons" or similar, if they already exist, fine, otherwise I would love to see them :)

Enemies/Environments
What can i say, you did a great job of making these diverse and interesting, very fun stuff!
What I can say however (i guess this is something you are already working on) is balancing the enemies a bit, some rare monsters can sometimes feel like end game bosses while others just gets one shotted.

Trading
Haven't been able to go online yet so didn't have the chance to evaluate this at all.

As I get the chance to play Wolcen further I will update and add to this list,
thanks again for a great game and hope to see it grow going forward!