Hey there! First of all I wanna thank you for the really detailed comment. Appreciate it.
For the levels, we had much more ideas but we unfortunately came short of time to implement all of them. Spikes and boxes were the only two things we were able to add out of all the ideas. And in the short time, we came with the best permutation of spike pattern we could think of that was challenging. We tried longer countdown but noticed the player is able to just walk right through. Was there a better permutation? Probably, but we sucked the math to think that through in such short time :')
Keeping the level paused and not starting countdowns until the player moves is an interesting idea that we never thought of. I would definitely consider that for the future, thanks!
The music is a good point that we considered as well. We knew it would be better if somehow the music was persistent between levels and continued to match the countdown bpm even when the level changed but unfortunately, we had no idea how to do it. Even right now, when the music restarts each level, halfway through the song, the music desyncs with the countdowns and we honestly don't know why. We definitely need to look into that aspect of how to match the gameplay frames to a song.
Overall, I think we just really mismanaged our time but we came up with the best we could in the limited time. Thanks again for your detail analysis, we will definitely consider some of your points for the future.
By the way, as for your point about top down 4 directional movement, the other dev working on this game has already made a game like that. If you're interested, you can check out his game, Cellwalker :p