I was annoyed. I only actually played this game once, and it was going so well (as I said months ago, I was at 123 and had barely a problem), so I stopped paying attention for a little while. I went back to looking at it maybe 5 minutes later, and there were enemies everywhere and I was done like a minute later. Maybe I should have paid attention and started adding some weapons.
343, I shit you not. The key is, after you get your basic guns built, to put a bunch of the stun things at the begining to slow them down and create a bottleneck, then build more guns and a LOT of damage increasers. Don't spread stuff around--concentrate it, but make sure the enemies are stunned (slow).