This review is from the perspective of someone who has never played FPS games, nor is good at them.
I really enjoyed this game for the time I played it; the easy controls layout allows you to play with just your laptop (though, I should have played with a mouse so I could move around the map easily) and is well optimized. My dingy laptop didn't have any issues running the game at a consistent speed! I love the work put into the sprites and textures; the cartoony enemy sprites clash well with the realistic textures of the outside and demon world.
This game was clearly made with experienced players in mind, so this next paragraph is simply based on my own experience. I think having a difficulty option would be nice for those who may not have a quick reaction time; I think the beginning level is fine in terms of enemy placement, but the enemy snowman blended in a lot with the snowy areas. I never found myself dying to them, but when you get swarmed by 3 or 4, you tend to forget where other enemies are placed on the map, and I found myself getting sniped.
If I have more feedback to give, I will come back to this comment and update it as needed!