Just beat it. This is 100% in the category of "Really cool ideas are at play here, even if the tech or design cues aren't entirely up to snuff." I still love what's here.
Gameplay wise, you can definitely tell in the latter half, that the creator's sense of difficulty and design started to dim a bit, mostly in terms of the fact that the lategame dungeons are generally straight lines with slight deviations here in there with very little reason to actually kill enemies. This dimming of design, however, is supplemented by what I think to be absolutely visually pretty design, from the beach, to level 7, and level 9 especially. There's a lot to like here as a historical piece and I recommend it to anyone looking to play something made so far back in ZC's history.
Fair warning for anybody willing to hop in though, Level 8 has a very mean instance of a compat bug with the lens not telling you about a push block that's integral to progression. For those who need a proper nudge in the right direction: Push the Bottom Left block in the room next to the Bracelet 2.
Overall, I see potential here, but it could have been much better with just a little extra effort.
In general, I do think you're judging the "effort" behind this quest under an incredibly modern lens that's not really built for it. If we're talking about the earliest quests in ZC's history, then we're entering ZC as a hobby in its purest form. Stuff like the continue bugs and the map issues are explicitly 1.90 compatibility bugs (Or just regular 1.90 bugs backported into modern ZC... or just formal oversights in the case of the whistle taking you to level 9?). These issues are not the product of a lack of effort, but rather, very real fundamental program issues at the time. Stuff like the ladder issue as well, are simply hobbiest "If you understand the program, then you understand how making the ladder on screens work, and that's just tedious as sin sometimes." I've worked with ZC for long enough, so when it comes to issues like that, I generally tend to just have a little bit of suspension of disbelief in this regard.
Also, it doesn't help that I legitimately ran into zero of the warp point issues you mentioned, and it's genuinely confusing to me (I was playing on 2.55.9 though, so maybe there's a ZC version difference causing problems?). With that said, I know scrolling warps in 1.90 are completely fucked up and impossible to work around, so I would not be shocked if they were here.
I think where this quest stands out and shows very clear effort, and where the creator's strengths clearly lie, is in looking visually interesting. From the miniscule changes to the classic tileset, to all the new tiles here, and on top of that, there's many cool ideas that can be used to inspire other people's future projects. I think Level 7 is a good example, honestly: It's a dungeon that has both indoor and outdoor sections, and while the tech wasn't there to pull that off effectively in 1.90, I think it can be agreed it's frankly a very cool dungeon idea. I think the quest is chalk full of small stuff like this, and I think it should be looked from that standpoint. If you see an idea that can be done better (And trust me, almost every idea here can be done better), then I think it's the perfect fuel to get inspired to take those ideas to heart.
The last bit I need to mention is that I think in the things this quests accomplishes, it should be pointed out when this quest actually came out. Specifically, it predates many of the best 1.90 quests of the era, and while it largely does its ideas worse than those quests, there's still value in a quest that does them first.