It gets reaaaallly hard around I think it was Wave 6, but I absolutely love the gameplay. I thought about doing something along these lines for the jam but I'm glad I didn't because you executed it brilliantly.
I have to agree with you. The combined waves of 5 and 6 are too overwhelming for the average player. The rest of the game was well made and balanced, but the difficulty curve was a bit steep and impacted the overall quality. Nice game though. 7/10