My suggestion for this incredible game is quite simple, and possibly already in the works. It also is a spoiler so be careful reading.
Anywho, for endless 1 (bonus mode) I figure there should be more rewards for how high you get in the wave count. Wave 50 is hard enough, and I kinda gave up (attacked my healer didn’t bother respawning), but maybe wave 75 gains another mass number of xp and wave 100 is another book etc etc.