I feel that the retreat cool down is a bit much, level 10 and I'm losing units just because they don't understand immediate death is 5 feet forward. Wouldn't be a huge issue if Class-D didn't have a cool down since them dying = no resources which in turn means failure.

Kind of hard to gauge the flow of enemies so perhaps a timer for waves would be a great quality-of-life addition. 

Great game in the making otherwise, just needs a little smoothing. <3