Wow!
Nice work in here. It kept me on my seat for about 45 minutes, as my first 2 tries lasted 'only' 14 minutes. I just had to get the final 15 minute badge ^^. I think all it needs is some more upgrades. Maybe some other weapons to pick. For instace you could choose to pick another weapon at certain weapon lever and change into that, or keep the one you had before.