What Electo said... Otherwise, nice game, but the unbeatable boss makes it unenjoyable. Basically, that level counts not on skill, but on powerup luck, which depends entirely on where the bugs spawn. If they're all behind the boss, you're toast. So, 3/5 (otherwise would have been 5)
Nice strategy: equip a noble or ranger with a rapid fire bowgun, and put the impact mod on it, then level up the penetration. Keeps most things at bay.