Great take on the reverse tower defense idea, the unique targeting for different enemy types is a really good basis for a puzzle game, the actual targeting for each tower was really clear once I threw my units in, no text tutorials needed. You even managed to keep the puzzles inventive enough that I wasn't really using the same solution multiple times in a row, really good work given the 48 hour time period!
A shame about the lack of audio, I think with some more enemy types and a some sound, this could work really well as a full release. My only real criticism is I think the "Pure Evil" flag could show up for a fixed "Maximum" amount of possible units for each level, since some levels make it literally impossible to save everyone. (Nevermind, this was a skill issue!)