Wow, the game oozes with retro charm - from the art, to the music, to the gameplay. I think you brought it all together in a very nice and neat package that makes for a blast from the past. I especially love the brick sprites you made for the terrain/background, they look really good and organic.
Design-wise, I have some thoughts. Some of these are just constructive criticism, but I understand some of them are hard to avoid because you're under a tight deadline. Just some stuff to consider for the future.
- I noticed I was still able to play the jump sound if I hit space while in the air
- I really enjoyed the SMB style of having the key follow you to the door, that was a really nice touch
- I'm guessing you're using a capsule collider for the player, which is generally fine, but with some pretty tight jumps like this, I had a few times where I ended up dying because I slipped off the edge
- You filled out the space very well, I didn't feel like I was cramped, but you also avoided making the rooms feel excessively big
- The committed jumps are a bold decision, which I don't mind, but certain levels like floor 4 give very little room to be able to get a run going and properly aim for the block. Combined with the third point, could prove to be a bit frustrating for other players
Overall, it's a short but sweet taste of nostalgic, retro goodness. Good luck with the rest of the jam!