A great game concept that has a unique set of strategies. My favorite wave is a swarm of goblins followed by the uh gnoll? yeah gnoll. The monster that gives shields to nearby monsters.
I'd love some kind of cooldown reduction with monster synergy. I beat the demo, but I was having issues getting my troops to stay clumped due to the inherent long-cooldown nature of the bigger monsters. I got to a point where buying monsters was not a good idea because their cooldowns would throw off the timing on my line-up. The last half of the game didn't include much buying because it would be disadvantageous. That might be the intended gameplay, but the game entices me with the store at the start of every level.