Huzzah~
Anyways this was really good and IMO the best of your three puzzle games that I’ve played. The puzzles here are clearly a few levels more developed that what Bubble Butler offered (still love the central mechanic in that game, but sometimes the puzzles felt a bit “okay, now try this slight variant on what you did before that prevents the previous solution from working”) and it has been good to see how you’ve grown in this regard. Heck pretty much all of your design has taken a big leap here, it can be poisonous to suggest to a hobbyist that “you could charge for this!” but I’d say both the quality and amount of designed content (hate that word, can’t come up with a better one while typing this) is at a professional level.
It can be hard in a puzzle game fifty stages long to keep everything feeling distinct and not like one is repeating themselves but you legit kept the variety high throughout. I do think some of the older puzzles sometimes have a bit of a different “flavor” than the newer ones (ex: 29) but they generally mesh well together and one rarely feels like they are doing the exact same thing they did before. The closest the game comes to it are some of the recursive numbers ones, and even those have enough differences from one another that they remain fairly dissimilar.
I worry seeing some of the puzzles previously might skew how I perceive the difficulty curve but I do think by the early 20s it takes a bit of a leap in terms of challenge and just keeps it at a consistently high level the rest of the way (it does let up off the gas around 40 for a bit, for clear reasons). I think having a few more moderate stages sprinkled in during the back half of the game would have been nice in an ideal situation just to give the player a chance to catch their breath. While I like a tricky puzzle it can be a bit exhausting when you just completed another very difficult puzzle and know it’s just gonna be that much of a mental challenge coming up next each time you do so. Give me one I can knock out in five minutes every so often, let me feel like a big shot for a moment 
FWIW, I was stuck on 50 for a few days and was legit worried I was gonna have to walk away at 49/50 complete feeling like a putz. It might actually be my least favorite of the fifty for purely personal reasons, it felt much more open in terms of what was asked (in terms of less being guided by what the puzzle presents and instead being given a goal and somewhat blank slate to have to craft a solution in) and I am much less partial to that school of design (possibly because I am bad at it). Clearly it’s not actually open as I’d wager there’s likely only one actual solution which is still hidden behind a linchpin (once I got said linchpin I went from “I’ve been stuck at two gates for over two days now” to “oh it is solved” within minutes) and there are a few clues the level layout does provide, but I probably went through a dozen or two other ideas before I got to that one as there were just fewer environmental clues to let me work backwards from and my brain just generally works much better in that direction for whatever reason.
I wrote that up not because I think it is a badly designed puzzle (it clearly isn’t), but on the off chance that reading how parts of it altered how one player experienced it is in any way useful. That and said puzzle has been bouncing around my head for way too long so I need to expunge all things related to it >_>
Anyways that personal hiccup aside I’d say it was a rousing success! There are years where this would easily be my puzzler of the year, it’s a great set of mechanical concepts you proved to have a knack for getting to bounce off of one another in very clever and creative ways. I’m glad that this has been your most successful/played game as it is certainly well deserved.
Now to give my brain some time off to recover.