I like the game but I think to complete the game its better to haven`t max upgrades. Because for not so good players this would be the possibility not to try 30 times to finish the boss. I always found it motivating to get upgrades after dying but when I reached the maximums there was no more motivation which I didn't like. I also didn't like that you couldn't see the boss. You could still find it with the cross but the best tactic was to just run in a square from corner to corner. Maybe you could have made the room smaller and the projectiles slower. To see your beautiful boss ;-). Also, it would have been cool if the dead players increased the rate of fire for a short time when you walk over them. What I didn't understand was that you had to go through the small room and it didn't restart immediately.
But overall it is a good and fun game.
Good job!