Hey this was pretty good! Challenging but not too difficult. Overall I had a good time though there were some issues.
I really liked the aesthetic of the Hub, Course 2, and Course 3. Course 3 was my favorite by far, that was so fun and beautifully modeled too! It felt like such a happy snowy village. Plus who doesn't love some Kirby 64 music? I'd say that was your strongest stage, with Course 1 probably being my least favorite, though still fun.
The star challenges - wow, there were some really creative ideas here! Some of my favorites were the chilly underwater dive in Course 3, the triangular walljumping in Course 4, the water level changing room in Course 2, among some others I'm sure. Those 3 were standouts for me; very interesting to play!
For the most part I was happy with the level design, at first I thought some paths a little tough or tedious but then I looked it up and you do mention that it is intended to be an Intermediate hack, so I just had to suck it up!
In some cases the modelling/texturing didn't make it obvious enough how to progress, a little differentiation in the texturing can help in these situations (especially areas where you progress by walljumping, use different textures on those spots or at least provide some indication, otherwise things can blend together too well).
The star hint names were pretty ambiguous - if that was the intention then no worries, otherwise on a few stages I was pretty lost as to where to look for the star. A few misspellings too, but nothing serious.
Oh, and the sideways floating castle in Course 4, I had some serious problems with softlocking on that thing. I'd maybe make that texture non-slip as I imagine the challenge is more about actually getting to the castle and less about sliding on it in a specific way, or maybe I'm totally wrong there.
Lastly some texture seams were present that could have easily been fixed. But like aglab2 said, it doesn't ruin the hack.