I decide to go back to work on my 2D platforming game. I need to finish what I've started.

What I'm still confused about is the level design. It's what made me burn out and quit.

Do we have a theory about it? If not, maybe I should play a lot of platforming games to get some inspirations.

for myself, I tend to 1) try to find other games of similar genres, and see what they do, and 2) I like to draw it out on a visual document (like in krita or gimp) or piece(s) of paper to visualize how it might play or look in the larger scheme of things.

this advice could go for any genre level design i feel, but i did try it on (platformer on unity i abandoned for different reasons) and i got more playable / interesting levels this way.

I have found that level design is very much a skill that takes lots of practice, at least it has for me and I’m still not very good at it. I think @DeanOrTori’s idea of visualizing the level and how it might play is a good idea.

Another thing I might suggest that has helped me with level design is to design the level with a single “path” and then add additional details, paths, and polish afterwards. Most of the games I’ve designed levels for I start with the “intended” way of completing a level and then build interesting alternative routes and secrets afterwards. It does take a lot of iteration though, which can be time consuming.