Not very original but gets the job done. I think the lack of sound effetcs really hurt the overall game feel and shouldn't be overlooked.
Different types of enemies would've been nice, but there's only so much you can do in 48h!
I also think the difficulty is way too high right from the start, I would have liked if it would ramp up more gradually.
Otherwise the game looks very good and it is nice that you introduced a little story to engage the player. The game feels good to play, the controls are fluid.
Good job!