Hey there! I got to 13th wave. The game is a lot more fun now and the headshot mechanic works well. New effects feel nice. Changed hitboxes made the game less frustrating, I actually opened the whole map and ran around well. Can't say that weapons feel very different from one another, but I enjoyed shooting.
However, I think there's a problem with zombie hitboxes, I guess that you use the same hitbox for damaging the player and the zombie, so when you shoot you can miss the zombie's model, because hitbox is a bit smaller than it. Anyway, that's not a big deal. Maybe, you should make melee attack a bit longer.
Waiting for updates with new cool stuff.
And I want to say that MG42 is an absolute weapon of destruction.