Many Monk, Demon Hunter and Barbarian builds use Vengeance, Epiphany and Wrath of the Berserker and have it active 100% of the time, which means that you do not see your Character with its original appearance often, even if you would want to.
On top of that, the visuals for Vengeance and Epiphany do look very bland and just dark, with the visuals for Vengeance dating back to a time where every DH build used the Natalya Set, which is why the DH in Vengeance form uses the silhouette of the Natalyaās Sight Helm.
Vengeance (current version, dark and bland):
https://imgur.com/Kko3EEz
Epiphany (current version, dark and bland):
https://imgur.com/kuBhmGS
To me, these visuals do not look very satisfying (and I know that many others feel the same) and thereby make the game less satisfying to play, so improving these visuals in one way or another imo would be a great Evergreen / long term change and not just something that last through one season.
The visuals of Wrath of the Berserker look more sophisticated than Vengeance or Epiphany, but still many people in the community do not like the āSuper Saiyanā-look and that the Barbarianās armor and appearance is disappearing / overwritten while the skill is active, so maybe these could be adjusted as well.
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Now that I mentioned the problem, I wanna suggest one possible improvement to update the visuals of these skills and one alternative way of dealing with it:
One way of adjusting this could be that when you activate these skills, the character keep their original appearance, but simply add something like a more transparent layer of moving particles (like a glowing aura) around it. Think about some variation of the aura you get from wearing a Full Set in Diablo 2, just with different colors and a different glowing effect.
D2 - Aura from equipping a full Set:
https://imgur.com/61yEHDr
Another possible solution is to allow players to toggle on and off the visuals for these skills.
But that are just some suggestions, so maybe the devs can come up with better solutions.
Thank you!