The idea itself is good, but some errors are going on. It seems like the web version is unplayable, due to the fact that I can not play again. After I die, I press play once again, and it automatically pops "You Lose". The downloadable version doesn't have this issue.
One major problem that the game has that I believe is very easy to fix is the enemy speed. You can make the speed of the enemy to be lower, so that players can survive for a longer time and can evacuate safely. Moreover, remember to normalize the speed/move vector, it seems like you forgot this, thus the diagonal speed is must greater than horizontal or vertical ones.
Honestly, I can still visualize in my head what you guys intended to deliver to the players - a cod zombie with math? Neat enough to be honest. Keep up the good work, and I wish you guys best luck on future projects!