Mars 9 postmortem type dealio

Mars 9 is a short platformer about a robot created for the LD39 compo.
It can be played hee:
While I'm really pleased with how the game turned out there are a few things I would like to have done differently.
What went well?
- I managed to actually finish the game
- I'm pretty pleased with the main concept of the game
- This is the first game I've ever made with a proper design document
- According to the reviews the game looks and sounds good (Fun fact: All the game's graphics could theoretically be displayed on a real NES)
What went slightly less good
- The game's really unfair at times
- The thing's too bloomin' short. The game was originally supposed to have 16 levels split across 4 acts. Well, that didn't excactly happen now, did it? (As a matter of fact the two songs that play on the intro stage were created as stage music for acts 2 and 3)
- Those bloody blue enemies! Why did I put them there!? They're not fun, they're just in the way!
- I should have created more enemy types to make the game a bit more varied
What went waaaayyyy down the toilet?
- I spent the vast majority of the voting time at the scouting Jamboree in Kristianstad so I haven't been able to rate very many games leading to mine barely having any at all.