The game is great, but that 2 summons are barely do anything. Skeletons are playing tanks, which means they're pretty worthless too. You need to balance their stats i think. Plus add some damage indicator(numbers or a health bar) to see how many damage you deal and to be able to tell whenever enemy is going to die soon or not. And of course add more skills;)
My last wave was 43. And damn that's hard. Levels just stop coming up so i stop healing over time.. and bam.. dead. Oh well, not going to go through that hell again.