The first few levels were a lot of fun, and I really loved the gliding mechanic. The purple level in darkness was pretty tough, but the yellow temple place... It's evil. That level... it's frustrating. The double hallway of retracting spikes at the start force you to wait fifteen odd seconds between runs. Then the level repeats that setup again later with more tightly timed variations, which still aren't fun. And then when you get through that, there's a crazy fast worm that I simply cannot pass alive. Difficulty can be fun, but this is grinding, it's repetetive and relentless, the challenges are *mostly* arbitrary (essentially just waiting) but if you mess up, you're thrown all the way back to the start. Then just to tease you, I'm pretty sure that the second health pickup in that level is impossible to get without taking damage.
Needless to say, I'm pretty salty. With that level, I'd recommend removing the repetitions of the obstacles. Each little challenge would be repeated a few times, meaning you needed to clear it not just once, but multiple times. For example, there was a part where you had to go down, then up and back down again. On the way up, you repeated the exact same jump five or six times, then on the way down was a challenge that was copy-pasted a few times. If you want to make it hard, at least vary the challenges to keep it fresh (and preferably avoid cycle based things like the first double set of spike hallways that you need to slowly advance through). The whole waiting thing at the start of the level hurts the soul, and I often relied on damage boosting to just get the wait over and done with.
Despite all of that, I did enjoy the first few levels. The levels were long, but the challenge was absolutely possible, and even with a few retries the levels were fun. There is a lot of good content here, I particularly love the graphics, and the mechanics are all very polished. I was impressed by the variety of the levels, with the different themes and obstacles. I wasn't exactly sure why the glide needed a timer, since I never found myself gliding for that long. Overall, the game was great, and if you were making a rage game, you certainly succeeded. The final level definitely has me salty, so that is at least part of the reason the review started off so negative (sorry bout that). Congrats on completing such a beautiful game, I love the character art and environments!