Altough it was quite easy to get into a "Survive? - No problem!" state, I observed your system a little bit closer and want to appreciate some specific points:
It seemed that you tried to balance the enemy strength regarding their move speed and spawn rate. At least it seemed so and I like that.
The idea of fusing dropped materials into traps is great. Especially due to the fact, that I did not had to learn several reciepes by heart. You made a price list and told me, what I have to pay. What I liked very much was the idea of choosing the levels in the first place instead of leveling up after the first build. Maybe a lifetime for the traps, a duration or a number of usages would have make the game a lot more enduring. A lava trap on Lv5 on the enemy spawn instantly lets you win the game. But hey, classic jam issues, don't worry.
The shooting precision seemed a bit off for me. Did the enemies (specifically the slimes) had smaller hitboxes than their meshes? Or am I just a bad shooter?
Anyway, it was an interesting system and I enjoyed exploring it. Has potential. Good job.