I wasn't able to complete the playthrough due to zombie being a nigh unsurpassable obstacle. The first one killed me like 5-7 times, and each time I had to make my way from checkpoint through all them fire hazards just to try some other method on it and fail. The zombie is faster than player, great at pathfinding, hits hard - approx 4 times and player is dead - and there is seemingly no way to put it down for good. Gun only slows it down a bit for a short time, at best freezes it in place for a second or two  if you use all charges at the same time. All of this coupled with narrow corridors made zombie a real barrier. Though I have to admit it might be a skill issue on my side.
At last I've surpassed the first zombie by luring it into one of the far rooms from which it had difficulties exiting for some reason. Second zombie further in the game seemed to not have such weakness, so I stopped there.

Other problems:
- gum gun has only 3 charges and needs to be manually recharged if those are spent in quick succession, and after recharging it might not fire right away for some reason
- flaming pipe traps damage player from a great distance, like 1.5-2 meters away when seen from the side
- health UI isn't super intuitive: long green line isn't health but some pulse indicator
- pipes require two shots from the gun to neutralize, and it seems like they reactivate after some time. Replumbing them is a bit annoying due to low rate of fire

On a more positive note I liked space setting, and gun idea is great!