level system:
This gets praise for some reason, the skills you pick are just "2% better at this" x times, except for 3 skills which you activate but those are just: ", 30% this now for x time"
So the leveling system doesn't bring much to the game and hinders you both in pve and pvp.

Map menu:
It kind of throws the maps at you and you are meant to pick one, hovering over them recommends you x amount of players and x level, i think they should be in order by this, because the first one is the newest map and it's definitely not meant to be for new players.

Gameplay:
The tutorial could use a makeover, and less unnecessary speech. (The tutorial throws too much ♥♥♥♥ at you in the combat areas, it's especially horrible in the zombie tutorial where you have to fight like 1 dozen soldiers which kills you fast so you have to respawn like 10 times before you can finish the objective and move on.)
The AI of zombies and humans isn't good, they really are just threatening in cramped places, they are fun to shoot but it gets old pretty quick.
The movement doesn't feel good, i feel like you move too slow, which is probably because the zombie ai is so bad this adds artificial difficulty.
The weapons look nice, amazing reload sounds, some don't feel good to shoot because of their damage, which you fix by using the bad leveling system, so just a hindrance.

And that's about it, because the game is pretty boring and i can't force myself to play more, i played because i wanted to satisfy my long curiosity for BrainBread 2.