Thanks for the kind words! I crunched the levels on Monday night, had maybe 3h of sleep that day :D not recommend. I'm super glad you enjoyed them though, appreciate it!
Nothing too fancy honestly. Most of the levels I placed stuff semi-randomly first, then played it once or twice to see what happens with the ball, then went back to level design to make it a bit more interesting, then playtested again, moved stuff around again, rinse and repeat until the level felt like fun, not too hard and not too easy, and doesn't look like shit. I also tried to incorporate some unique mechanics every 2 levels or so, so that it progressed incrementally.
In the end I'm proud how it turned out :)