i couldn't figure out the passcode for the door because the numbers i got were 7007, and the 7's really looked like P's. I thought that someone had written poop on the blackboard so i ignored it until i watched the walthrough. :D
i did the last level hard with 3 meteor cannons and 1 homing missile. The 2 center gun slots shoot diagonally so i put the homing missile on the left center one. This allows you to have higher straight forward dps. i found that 2 homing missiles in the center slots was too weak, but with just one homing missile it seems much easier
You can do it! Thanks for playing mithrindir!