The days are too long. It's really frustrating to spend a lot of time getting through 10+ waves to have to restart. Shorten the number of waves and increase the number of days.
@hooverboy - Don't build so fast and/or don't include every minion in your design. Buy equipment for your adventurers. Adventurers gain HP for every tile they step to so include lots of long halls so they can regain HP between fights.