I jumped right into the game and completely missed the BIG BOLD text right underneath...completely my fault. I did exactly what your friends did haha.
Wow! I really enjoyed spreading the corruption though reminds me of the Zerg creep spread in Starcraft. Probably would have been harder to implement but I think a tutorial level would have helped the instructions sink into my brain more. I tried to remember all the directions being given but it didn't quite stick once the first level started. The additional buttons over the minion units though were super helpful.
The music sets the atmosphere really well. The art is absolutely fantastic, loved all the sprites.
The game felt like a cross between a puzzle and RTS game. It felt like I would run out of resources and that I had "failed the puzzle". The moments when a chicken would just waddle onto the edge of my creep and save me though were so great.
The game loop was fun! I almost feel like I would have enjoyed seeing the creep continuing to grow and "discovering" the other life instead of resetting everything and having them introduced per level as a different puzzle mechanic. I realize that's mostly personal preference though :P
Regardless, really liked the game and felt super polished! Would have never guessed this was your first game jam.