The difficulty is perfect. People are too use to games having an "easy" mode. The biggest problem I see is the bullet mods are way underpowered, even if they were 1 point each.
I really liked this game at first but I was waiting for the map button to light up before moving on and when I finally did I didn't have enough ammo and died. When I continued it put me on the same level and the waves just kept comming until I ran out of ammo again and died. I tried a new game but it's now bugged so the 1st level just keeps throwing waves at me until I run out of ammo. Now what do I do?