Being new to Vermentide this is my thoughts:
make it possible to skip the whole chest upgrade thing after game. PLEASE.
implement numbers, or percentages. for me, seeing any talent or alike where the hp is modified in a number is meaningless. i have no idea how much hp i have, hence i do not know if 20 hp is a lot. (it is if the total is 25 hp , not so much if the total is 1000 hp). i know its me being a noob, and i can do some testing to find it out, but its an easy fix and new players shouldnt be required to do testing imo. or make everything %-based, so the numbers dont really matter.
make a scoreboard ingame, just like the one at the end of the game where u can see dmg dealt, dmg taken, etc. but just live, and ingame.
make a Mythic+ score (from WoW) similar system, to make sure people will keep playing. for some people, grinding is just fine as long as u can beat others while doing it or show off a cool rank. this (proably simple) thing would give alot of replayability in the game without making anything actually new. (im getting a m+ish feeling from the heroic deeds, so we are already nearly there i guess)