I didn't mind this one. Although I figure that any manga I actually finish had to be interesting in some way if I stuck around for nearly 200 chapters.
The premise is fine, a "weakest [blank] is actually the strongest" isn't the most original thing, but I came here for the ridiculous over-powered abilities so I guess it's alright. The characters were generally likable, although I've never liked the dense MC trope since it doesn't add anything (especially here) so I could've done away with that for sure. But what drew me in the most was probably the overarching mystery—specifically why the blue crystal monsters were around, and the existence of the three 'bosses'.
The one critique I have about that though is that I wish we had more time with them, learning more about their personalities, their goals, and even their powers. All we really got for that was a brief panel with them as humans before Aria's introduction, so I thought that was a shame. I would've liked to like these characters, but they just felt like milestones for our protagonist.
Other than that, after looking through a bunch of comments, with people being extremely dissatisfied at the ending, the obvious reason as to why is because it finished on a cliffhanger. If the 'blue crystals' arc was treated more like the main story and the ending was wrapped up neatly from that, not nearly as many people would've had a problem with it. I'm sure the author knew that was the risk for an ending like that though, so not much else to be said about it.
(Though there's a little comment right at the end of 163 that says that the final volume "will be released on January 9th" so it's not where this story was supposed to end anyway.)
Overall, 5/10 — kills an afternoon well and had some great storytelling moments, but there's a lot of missed potential. If the final volume ever comes out, then I'd like to see where they conclude it, for sure.