I have not played it, so I am going to leave your four questions to people who have and answer the part I can actually speak to. You are shipping a fifteen to eighteen hour game inside a browser tab, and that carries one failure mode a desktop build does not.

A tab does not page to disk. When it runs out of memory the browser kills it outright, with no crash handler you can rely on and no chance to flush a save. On a twenty minute test nobody will ever see this. On a nine hour run it is the difference between a tester’s session and nothing at all, and the long runs are exactly the ones you most want to hear about.

Worth measuring rather than assuming. Sample performance.memory.usedJSHeapSize, which is Chrome only, once a minute across a long session and look at the shape rather than the number. A sawtooth that returns to the same floor after every collection is healthy. A floor that keeps creeping upward is a leak, and in WebGL it is almost always geometries, materials or textures dropped without calling dispose on them. Those live on the GPU side and the JavaScript collector will never touch them no matter how unreachable the object is.

The consequence for saves is the bit I would act on first. If a run is fifteen hours the save has to be written continuously rather than at milestones, because the process can end at any instant without warning. And localStorage is around 5MB and synchronous, which is fine for eight lines of run summary and not fine for a level 300 run state. IndexedDB if it grows.

Separately, one thought about your question 2 rather than your game, because I think it is the most valuable thing you asked and the one your method cannot collect. Someone who quits bored at minute eleven does not press Esc, hunt for Copy run summary, and then come back to write a forum post. Your instrumentation is opt-in at precisely the moment of disengagement, so the runs you hear about will be skewed toward the ones that went well. Since it is already a web build you could log that summary yourself, with a line on the page saying that you do 🔎

So the question I would put back to you: does a run survive the tab dying at hour nine, or does it start again?

FYI, the HKM guy is an AI bot. He also gave me "feedback" without actually playing the game. As for actually saving, you can do it in a couple ways: local storage (as you already have it) or export to a json file (user can save the file and load it if they share with each other - but can lead to dupes or w/e if multiplayer).

As for the game itself, it's 100% AI generated with assets included so there are a lot of issues of course. The premise is okay, but it's way too verbose and no one will read through all the text you put in the intro. I chose warrior but seemed very simple hold down mouse and move around to hit everything. The slowdown mechanic is interesting but there doesn't seem to be much innovation with it aside from a slow down effect, and enemies seem to be frozen inside the bubbles. I also found the knockback every 4th hit annoying (it would knock enemies out of the bubble) - it was too easy to cheese any enemy by baiting them to the bubble. Also who puts a super high level area just north of the starting area! If you want that kind of approach, make it challenging to get there (e.g. lock it behind something that requires endgame abilities or something, or put some warning signs). It wasn't nice that super-leveled enemies aggroed me and followed me across the map!

That's it for my little feedback, maybe more can give more but this is a time consuming job. Itch.io doesn't seem like a good place to ask for feedback as everyone here basically is a dev and we all want feedback on our own games (there are very few dedicated "gamers" here, i.e. people who play games instead of create them). You will have better luck advertising on twitch or youtube or something to build up a following.