I've seen a lot of "Tower attack" concepts, and this one has a cool take on it!
Uprgrading ennemies at the same time as your troops means you have to think about cost and risks.
Here, there's not a lot of options, but I can really see how you could expand on the concept!
Still, for a short game, it's really entertaining and I like the troops' designs! Great job to you two! =D