So I finished most of what this level has to offer at the moment, not counting the incomplete chapters. I have somewhat of a love/hate relationship with it.
In many ways, this is an extremely impressive effort. I recently played the original Azure Serenity and thought it was decent, but it definitely favored quantity over quality. This remake rectifies that quite effectively, with its hub retaining most of the original areas, but giving them far more polish, in addition to various new locations. There are a few spots here and there that I thought were still a bit underdeveloped, but for the most part, the level's world is far more memorable now, thanks to it looking a lot better and giving you more to do. It's no longer just a quick sightseeing trip through tons of different locations. It sounds quite nice as well. I wasn't the biggest fan of most of the Freeplay music, so I mostly prefer the replacements or at least found them equal in quality, though there were a few that were kind of weak.
The concept of individual chapters is also fascinating. With only one of them properly implemented so far, it doesn't really work at the moment, but if this level gets finished, it could make for a really interesting experience to alternate exploration of the massive hub with occasional adventures into entirely new places. The magic spells are also intriguing. Again, with only one of them available at the moment, this concept doesn't really work currently, but being rewarded for completing chapters with the ability to occasionally make certain challenges easier sounds like an interesting way to implement long term progression.
But in terms of difficulty, this level is clearly aimed at more skilled players than myself. It's certainly harder than Gustav's Retribution. I don't really mind there being a constant element of danger, as it helps ensure that you can't just quickly walk past locations without anything really happening in them. And there were some occasional challenges that were tough but gave me the feeling that I could master them (for instance, I was handling the early parts of Shreep's Fungeon pretty well). But a lot of them were quite frustrating for me. There are some serious difficulty spikes from time to time that truly drove me insane.
The hardest individual challenge I encountered was probably the final phase of the Silver Priestess battle. The only solution I managed to find was to glide through two of the fakes from the top and then try to hit the real Silver Priestess. I couldn't really find any way to intentionally dodge the side shooters, especially since I needed to be extremely quick to pull it off before the flames were shot again. So it was largely just a matter of waiting for the perfect RNG. But the area I struggled with the most overall may have been Crystal's Maze. It wasn't too hard to reach Crystal, but I completely lost my way on the return trip and was forced to endlessly walk through the maze at random and waste a lot of effort overcoming challenges that proved unnecessary before I finally managed to somehow get out of there again.
As for other bits of feedback, while this isn't as much of an issue as in the original, there are still some overly bright or dark areas that suffer from poor visibility. Chapter 1's finale in particular was a real eye strain at times. I spent a long time trying to climb up the wall in the hope of finding something up there. I'm not sure if you actually can go all the way up before defeating the Silver Priestess, but if it's possible, I certainly didn't manage, as the tiles at the top were virtually invisible.
Also, there are still some voidscreens (or should I say whitescreens). The vast majority are the result of many places not being quite umbrella-proof. They're usually harmless, but I found two instances that actually let me go out of bounds (one of them was in the space area near the top of the hub). And two of the map cutscenes from the level previews are broken and send you to a whitescreen (I believe one of them was in Cinder Ravine's preview). I had to edit my save to get out of there.
Furthermore, this is a pet peeve of mine, but in levels that give you the map powerup, I like to completely fill out the map to make sure I've seen everything. The original had many screens that were impossible to mark, either because entering them resulted in certain death or because they were unreachable. The remake seems to have intentionally made some design changes to make it possible to survive various screens that previously killed you, but there are still plenty of unsurvivable ones, especially in Chapter 1, and a few unreachable ones. It can hinder the process of backtracking through old areas for the sake of cleaning them up, since I often can't remember if unmarked screens are actually places I missed or if they simply can't be marked. If you have any interest in rectifying this, I can share my save file. I was pretty thorough in filling out the map, so most of the screens that are left should be unmarkable.
Also, it wasn't a good idea to have the boss at the bottom of the ocean award you a golden creature. Since those have no flags, the level can't remember that it got defeated. What's more, the route to this boss has multiple obstacles that make it impossible to manually backtrack out of there, so if you return there, your only way out is through a rematch.
Finally, the only piece of fully implemented content I have yet to complete is A Midnight's Wander. It's an interesting idea that's a nice change of pace, but I can't say I like the execution.
It relies heavily on secret passages. Due to the lack of detector targets, the only way to find them is by wallhugging. Even that didn't work reliably enough for me, so I had to use the editor to find many passages I missed. I eventually managed to get all the hints and reached the labyrinth, but now I'm completely stumped. I must be fundamentally misunderstanding the rules because they don't really make sense to me. IIUC, I'm supposed to go through the hints in reverse order and follow the directions of the first that applies to the current room. And if none apply, I should repeat the directions from the last hint. The first room doesn't have 26 Cats, 6 trees and 2 rats, so Hint 7 doesn't apply. It has fluorescent lights hanging on the ceiling, so Hint 6 applies and I should go down. However, all rooms below it seem to have no applicable hints at all, so I just end up back where I started. In general, remarkably few of the rooms I'm able to find seem to have applicable hints. Hint 6 occasionally applies, but the rest hardly ever do.
Until someone can explain what I'm doing wrong, I'm completely stuck here.
Despite my best efforts, it seems I once again ended up writing a lot more about what I didn't like. I hope this doesn't come off as more negative than I intended. I still really enjoyed the core concept of this level and I'm very much looking forward to seeing more progress. If this level ever gets finished, it's going to be an insane achievement that really pushes KS to its limits. It's just a bit too hardcore for me to really fall in love with it.
Edit: Just a quick note, since I saw you do sub-optimal umbrella gliding in your playthrough of Gustav's Retribution. You can glide further by holding S. It's effective enough to traverse just as many empty screens horizontally as vertically. If you actually didn't know about that, then that explains some of the whitescreens I found here.