I remember reading this a few years back after reading all of its chapters, leaving memories of "man this looks cool and it has a lot of potential to shine"

This obviously hasn't aged well, only the looks stood up, and this is frankly a tragedy that the writing didn't get better, for my main gripes are structural to the manga:

• too much of the story follows "tell don't show" instead of the opposite, every few chapters we get long backstory exposition scenes that either:

- doesn't fit or contradicts a character, ability, item or area's previously defined or hinted characteristics
(ex: MC's self description says he's essentially stuck in a dead end job, delving low level dungeons for a decade, doesn't talk about the guild with any sort of affection(nor ever seems to have feelings or strong opinions),
but then we have one of the guild's staffers suddenly think about him out of nowhere and essentially say he's a generous pillar of the community that always helped newbies do much the entry death rate plummeted,
Wich is then further contradicted later by him being extensively cold and wary of a rather clueless newbie trying to scrape some money to save his Inn)
- Explains a major story element later, out of the blue that should've been referenced at least in any way, wich does not stick with what we learned
(Ex: in the same page before using spirit power, one only clerics, the blessed and a few others can do, MC explains that he did get that by a fairy, a power that would not only have allowed him to easily get higher than bronze rank, and never used it before in cases where he it would've been greatly helpful)

• the dialogue is clunky and bloated:

- characters will drop information they knew and so did the reader and MC, they had no reason to bring it
It's as if the writer forgot what he wrote a few chapters back and never bothered to re-read his stuff.
-characters can't for the love of god be subtle in their reactions, declarations or revealing dialogue, it's essentially:

Rando: "so something hapenned to me it was terrible a dog bit me and it hurts and now i'm scared another dog may do that and that's why i fear dogs"

MC, in internal monologue: "hmf, that's all? I was eaten alive by a dragon and now i'm undead and i've been ostracised and stuff yadda yadda(...)" - he said at chapter 5X.X

It's as if the mangaka never talked with someone before.
Overall, if the author bothered to re-make the dialogue and add indirect cues, reactions that implies something instead of just giving the information outright, he could've reduced the dialogue to half its size at least and given himself much more leeway to deepen the characters and world later on on top of increasing dialogue quality considerably.

• the story is disconnected and un-hinged:

- stories that goes nowhere:
at multiple times do we find mini arcs the MC does with a new character, be it with a new adventurer, an innkeeper or with a blacksmith, two lf theses are hardly mentionned and are just a tool for the author to add unfitting characteristics we've already been given before, and the third one is litterally an answer to "well where does he sleeps or eats
Two more story bits are how he had a cape by visiting a secret part of a dungeon, and finds way stronger people inside that gives it to him in exchange for him not ratting out, and despite MC telling himself he wants to check it out again, never does so. Same thing for the recurring quest to get dragon roses daily but is never even mentioned as if it stopped existing in the next chapter

• the characters, like the dialogue, is terrible:

- The MC possibly being a self insert is the least of its problems:
He seems to have no personality of his own, sadly a trait shared by more and more decrepit stories.
The majority of stories exposes and develop character through a drive, a goal and what they are ready to do/did to obtain it, it's less the chemistry between two characters. In this case our MC wants to reach mythril rank adventurer and possibly become human again, but his actions are not what drove his progression, he is so passive that the world essentially bends around him, facing no real threat that isn't defeated in more than half a chapter; his evolutions are subconscious, he cannot decide what he'd want, the second evolution was outside of his control and third he had the blood through pure coïncidence in a disjointed plot where he's asked to see some aristocrat family, none of these give any info on the MC's personality
- the other characters are nearly as bad but for how flat their personalities are, the sorceress is the most fleshed out of all the characters but it still resumes to her being lazy(but not because it's contradicted later) who's attracted by the MC for contradictory personality traits i've talked at the start. Other NPCs are so rarely shown that they haven't had time to show any if not for the innkeeper who's a hardworking man willing to risk his life in a dungeon with a smile if it means he and his wife get to keep their buisness up, hiding the pain.
All the dialogue bloat that could've been removed could've been used to learn more about each's personality and maybe have MC react in a way that it also show us info about him. This isn't the case sadly.

• the world is severely lacking in depth:

- dungeons are flat:
The starting dungeon is as bland as it comes, no sign of possible use for it before it became one, no machinery or lack thereof like ripped out pipes, it's all stone/marble with mobs in it
The volcanic dungeon is litterally skipped 2/3 in and is only used to have a dragon eat him and puke him out giving him rare metal bars
- the scale of the world is inconsistent and incongruous:
Every out of town locations he's been to seem to be within short walk distance from each other, including some desolate poisonous wasteland, to the point where it's somehow possible for a butler to go there every day to pick up a flower deep into the territory like if it was going to the bakery, nearby towns aren't even hinted about how far they were, enough so that the MC casually walks there, same for the sorceress's house or other locations. This world is tiny it seems or maybe everyone's walking pace is on par with a car, who knows? Because the author doesn't seem to know either.

- there is no stakes, no apparent difficulty:
- Anything too strong becomes a gift event:
Each time something seems to overpower him it's always a positive, from some stronger enemy seeing you as an invader casting fireball on you, but decides not to and give you potent gear if you shut up despite having nothing to gain and everything to lose by doing that, to an earth dragon eating him and actually puking him up unscathed and leaving the MC with rare magical bars only this kind of dragon could make somehow, to some vampire hunter trying to kill him but the second after throwing money at him, although a bit more fleshed out then the rest.
- anything not instantly overpowering him is beaten without any cost, no physical damage, no setbacks, no relations or outside environment damaged or disturbed, he's somehow so strong the main things stopping him is his own gear, they essentially come out of nowhere and dies as fast as they came, to be quickly forgotten, they don't represent anything to the MC especially when it comes to chara ter.
The mangaka seems to not understand why there are fights outside of putting up a show between two powerlevels, forgetting its original use: to have an antagonist not just in power but a clash of ideologies, personality, worldviews and also as an act to show personality traits to the viewer and nearby characters, it only happened once: at the very start when he just evolved into a ghoul, saving a newbie from a skeleton way under his level.

Right now, he is at a powerlevel most other mangas would reach at chapter 70-90 at the quicker side, lacking storybuilding elements most covered by chapter 20-30, this manga fits the technical requirements of "a retarded story", though it might lose that if the gap becomes so large it might simply lack a story altogether

-The art is comparatively great but it's wasted on drawing expressionless faces, simple environements and generic characters, very little time or space is used to have contemplative moments where you can burst with style and meaning

The author should maybe think about rebooting the entire story. ESPECIALLY given that he has caught the eye of an animation studio to animate his story.
It's never too late to re-draft when it isn't finished, your work can only improve if you review your work critically and decide to improve it.

If i was in charge of it the first things that would change is:

• a short 2-3 page résumé of his life the last 5-10 years in the first chapter
• a series of mostly out-of context images representing some of the things he has done of note, flashing before his eyes as he's about to be initially killed, that will be of importance later and links it to his progression
• either have him lose some memories that he'll randomly remember in parts during his sleep, intrinsically linked to previously established memories or past dreams, so that it explains why his character isn't exactly coherent with some people's description of him
• have him emotionally react to theses memories or have them drive him to some actions he did in the manga based on what he remembers or forgot.
• give him a survival factor to stress him a bit so we learn more about him as a human being (ex: as a skeleton he instead needs raw mana over time to not collapse, or to periodically need flesh instead of easily findable blood in a few daily drops, something to push him to make ethical choices or having to hide more from people, like having to hide while eating some meat to not reveal himself) and have people have a stronger reactions to having someone being undead.
• Have a map of the world or region with places he will go to later, and have each new travel have at least one small event or dialogue inbetween, give it time to breathe, some exposition on where they are going, personal worries or general observations about the world, we're talking about an adventurer who's done nothing but venturing the same dungeon for a decade, give him some curiosity given he finally gets to see something new.
• Cut half of the dialogue to get rid of useless repetitions, replacing part of it by insinuations, clues of how the person feels about a subject, so that if they actually talk about it it means they have invested interest in telling the MC about it. Replace the rest with either more detailed backgrounds or illustration to back up their words, or add more dialogue adding onto the story, info we didn't know, it can be inconsequential at first but it's free handles to hook onto later and really links the story together, adding causes and effects.

As a general conclusion: the art is good story is in shambles, its anime adaptation will either be as terrible or extremely different from the manga if he is to try to save it from being known as a mediocre story
Cialogue: 2/10
Character (bg, dev): 1.5/10
worldbuilding: 3/10
Artwork: 8/10