I like idea :D For me controls were fine when you get used to it you can really kill a lot of zombies :D
The only thing that I would like to see is some indicator that you syringe will break... Because now it just breaks and then you need to run from zombies until you deploy a new one.
I love the pixel art style and a very polished look.
Good entry for that amount of short time! I think it has some potential!