Time to ! PANIC !
some things that could balance the game out and make it more fun:
1 increase spawn rates at edge of the map, it is way to easy to just go around the edge of the map and stay there
2 make enemies get faster as their life goes on, this could help that thing where you blink and one popped up right in front of you and killed you. it would also help that staying at the edge thing, because when you get that long line of enemies behind you... they are no issue at all, with this you actually will have to take some evasive maneuvers and kaboom them before they catch up.