Thank you!
The plan was to make the heat constantly rise up but in a more controlled way, otherwise it would get overwhelming pretty quickly, that's why I decided to go for the shots and enemy deaths generate heat, instead of having it constantly go up.
The real "cost" is with the items, which give you health or damage at the cost of making things more difficult as time goes on.
I had a few more ideas to make it more interesting, unfortunately due to the time constraint we had, I decided to simply polish what I had as much as I could instead of adding untested / unbalanced mechanics.
I appreciate the input, and I'm glad you liked it!