Flip Knight

To be fair, I don't think I offered desktop versions of the game when this post was made - which has now been rectified :)

I've played plenty of hard game's and this is no where near the hardest, but I still don't think I'd called it "fairly easy", to you as the designer that's true I'm sure.

I'm very familiar with the idea of introducing a concept and then pushing it, it's used in just about everything, but my point is this game keeps testing you on some things well beyond the point where it's conveying anything new. Particularly, the rooms with the force bouncers (blue lines) and the moving spikes are what I struggled with the most yet of all the challenges present in the game, they also the least original in terms of the skills they test. If you've played games like VVVVVV I'm guessing they're easy, but as someone who hasn't played it these rooms just acted as a barrier between the interesting bits. It is only a small portion of the game overall but it's weird that they're the hardest part when all the terrain destruction challenges are never pushed to such a limit, instead enemies are just thrown en mass in it's final challenge which is more just tedious to deal with each one.

TLDR I think the "what if the player just lucks out" mentality is something that, from personal experience, it's easy to get overly paranoid about. 

Regarding the back tracking, there was one of two shortcuts I think I may have missed first time around which is my bad, but the final puzzle still seems a bit backtrack heavy whilst the actual puzzle is barely that, it more just exists as a way to force you to do the same bits over. I don't know if this is intentional but there seems to be two ways to go back to one of the grav switchers, but the one that I noticed any substantial difference in because of the grav switch I missed out on my first playthrough. Even then, it's still pretty much the same challenge. If this is done to internalise the concept then it's internalised to the point of getting a little uninteresting. 

Perhaps this all sounds overly harsh so I do want to point out this is quite high quality for a web game, but the design is something I like to think through even on smaller games. If you just want to ignore my over abundance of criticism feel free, I'm mostly doing it to figure out my own perspective on the game.

That said, I take issue with your line "Criticism is welcome but criticism is far better when you complain about specifics and what to do about them", because at that point it's asking the player to design the game for you. Surely it's part of the designs job to take in and interpret criticism. I don't know what audio skills you have and I've expanded about as best I can on where I think it's a bit too hard vs where is lacks difficulty. 

The only other thing I can maybe suggest regarding music is to perhaps experiment with a string of atmospheric sounds. In my game Rejection Thesis (Rejection Thesis by Brandon JS Lea (itch.io)) I messed around with a few synths just to produce some atmospheric sounds. There's room for improvement (they play on cues so if you're stuck in a room for a while it'll still be silent) but I still think it adds something to the experience and I really have 0 music knowledge. I bring it up because this game goes for a similar isolated alien atmosphere.