Well done on your game, and congratulations on making a complete on in the timeframe. It was short but sweet and although I didnt immediately get the hang of it it turned out to be a neat concept, some comments:
-I would not rotate the trees! The art looks great but by rotating them in the 'correct' direction it creates a bit of a wonky look, you can look at examples the like of pokemon, they all keep their trees upright.
-The game could use some more depth, perhaps the zombies and priets come in alternating waves, I am not sure, but currently the game just lacks that bit of extra diversity in gameplay (something of which I am aware I am also guilty of myself!)
-The audio mix is a bit off, the footsteps are too loud, which is a bit annoying
-The concept feels a bit forced, why are zombies suddenly running away? Perhaps a concept like 'you try to convert the survivor in a zombie survival game' would've worked better. (Although I do see that that is perhaps less creative.
Overall you made an interesting game though, with a concept that is definitely not often explored, well done!