First of all, thank you for playing it !!! It means a lot. :D
Yeah Level 3 turned out to be way too hard. At some point we want to revisit the game and release a better version with more and better levels. With Lvl 3 you have to find a rhythm of separating (one guy covers the bottom and one guy takes care of the top action. And getting back together to defend the upper door. Also when the fat guys spawn, be really quick to take them down.