When playing Full Game / Normal, I can't launch missiles. (Thus, my game comes to an end at the first meteorite storm). Launching missiles generally works correctly in Easy or Beginner, although I had them stop working mid-game on a Single Level Easy Medium Moon game. (It's also possible I misunderstand the rules: are there circumstances when crewed and powered missile defense stations cannot launch missiles? Do they get used up?)
Shouldn't be anything different between the difficulties. You do have a limited number of missiles per wave (4 per gun; they're displayed visibly and used up as you fire). The sprite's not very good, though; I may want to rework it to be more visible.
If that's not the problem, PM me and I can try to sort it out.
Some of the mechanics could be a little less opaque. For instance, when the meteorites were falling and I didn't have a missile tower that had line-of-sight on them, it just felt frustrating and confusing for a while. In fact, I felt pretty sure that I did have line-of-sight, once I figured out that that is what was going wrong. I might suggest drawing out the line-of-sight for your missile towers and indicating graphically or aurally that your buildings are in the way and so you are unable to fire. This would make it a lot clearer to the player what's going wrong.
Sure. It did that in the past, but it seems to have gotten lost somewhere in recent changes. (Drawing out a truncated line-of-sight.) I'll have it in the next version.
Audio is slightly harder, but it's a reasonable idea. It was on my to-do list at some point, but was never a high priority and vanished at some point. I'll stick it back on and see where it goes.
Also, when I finished the first tutorial, I thought I'd finished all of them, so I tried playing the full game. This game is impossible to figure out on the fly. That's fine, but you should make it clearer that the player has not finished all of the tutorials until they have, and then strongly recommend that they DO play through the tutorials. Make the default menu starting point be in the tutorial selector until they've finished all of them, perhaps?
That's a bug. Sorry. It's been a nightmare weeding out all the tutorial-specific bugs... it's supposed to route you directly into the next tutorial after you finish the first one. That must have broken at some point. I'll have it fixed in the next version.
Very sorry for the confusion! I'm pretty embarrassed that one slipped through.
EDIT: found the bug, it's about a day old. You chose the exact wrong time to start playing!
EDIT 2: New version is up.