Finally, someone who actually tried to use projectiles and enemies in a game!! Your depiction of the space invaders gameplay is spot-on! The increasing difficulty and the varying bullet speeds were nice mechanics too - it adds a bit more complexity to the gameplay. I also like the alien animations.
A few suggestions:
* Since you are banking off Space Invaders, I feel like this game is the one most wanting for sound effects. Add a few bleeps and bloops (very easy to do in TIC-80 even without music knowledge) and it would have added more to the Space Invaders feel!
* A level indicator would be nice - it would allow the player to receive positive feedback on how many waves he/she has defeated already. I know the score is already there but in games like this, it's also nice to keep track on how many waves you have overcome.
Great job and congratulations, you passed the TIC-80 course!