That was pretty great -- it took me a bit to understand what was going on: you need to intentionally place tiles with enemies so that the player will be able to level up. Once I understood that though, it became a neat puzzle to try and figure out.
A game about designing things feels like a tricky thing to design itself -- I'm happy with the way it was balanced because I was afraid I was going to get myself stuck and would have to start again, but luckily that didn't occur.