Just had a look at your game, I'm new to this as well.
I liked the block zombies, even though it's a few pixels on the screen, they looked like floating zombie heads coming towards you.
I was initially shocked by the speed they come in from the sides, but I think the game area and the player speed are a good match for this. Going with this speed, I felt the shooting was a little slow and would have liked to have been able to either shoot quicker or shoot more than 1 bullet every shot.
Otherwise, good start.