Pretty good
Level one was pretty simple, I was barely able to pull my ass over level 2 and I never was able to buy a factory...then BOOM I get to the armored ships in level 3 and I die horribly, the level skipping feature was nice since I couldn't beat level 3, Level 4 BARELY, just barely had enough ammo, I made it through with 32 shots left to my guns *Tip*, let the enemies shoot the door open when they can, if you don't you WILL NOT have enough ammo to make it through.