Made in Abyss is one of the very few mangas that I have read in one go, mainly because it draws you into its world through the use of its unique art, story, and characters. One moment the story will show the reader how twisted and disturbing the abyss is and the next will leave you in awe of how beautiful and epic the abyss can appear in certain moments.
Even making a dangerous man-eating creature appear majestic at times.

In terms of world-building, it was a good choice to flesh out the abyss and the island it belongs to as beyond the island is not all that important when it comes to Reg and Riko's journey, though it has been talked about a few times throughout the story.
Speaking of beyond the island, Bondrewd an antagonist and a wanted man from another country has become one of my favorite antagonists of all time.
(Have been obsessed with him for quite a while after reading, though most people who've read the manga probably hate him #bondrewdbestdad)

Bondrewd is a man devoted to knowledge and will stop at nothing to pursue it, sacrificing people as a means of acquiring knowledge and has become so warped that he cannot see the wrong in his actions.
Along with Bondrewd, the main protagonists Reg and Riko are very likable, Riko is brave and knowledgeable but physically weak and reckless.
Reg is physically strong and cautious, but at times acts cowardly and is emotionally dependent on others.
And both characters develop throughout their encounters in the abyss overcoming their weaknesses both on their own and through supporting each other.

Story 10/10
It may seem like a basic set up for an adventure story, but has many surprising twists and turns in the story.
Especially after the point, they meet a character called Nanachi in the story and dive into the Bondrewd arc. Though it was already pretty surprising before that point anyway with how the curse of the abyss affects people when they descend and the things that were revealed about both Riko and her mother.
Art 9/10
The Art fits perfectly with this manga giving it a unique look fitting to the story and can transition from light-hearted to dark moments effectively.
I also love the design of each layer in the abyss, each having its own look and creature designs unique to that layer.
At times it was hard to make out what was going on in a scene, which wasn't that often for it to be a major hindrance.
Character 10/10
A lot of well designed and likable characters such as Ozen who has more depth to her than at first glance and is a major link to Riko's mother.
Nanachi is a later addition to the main cast, who is shy and distant at first but is found to be kind-hearted yet haunted by her past.
Then there are the characters from below the 6th layer that all have strange personalities and have mystery surrounding how they came to be.
Also, many of the inhabitants below the 6th layer believe in the importance of possessions, a little more than they should. (my favorite being Majikaja)
Enjoyment 10/10
As I said at the beginning couldn't stop reading until I had reached the current chapter and had to wait for the next.
Overall 10/10
A must-read for fans of fantasy manga, though don't be fooled by the cover, this is by no means a light-hearted read as it contains quite a few disturbing scenes and dark subjects. And the deeper they go into the abyss the darker it gets both literally and metaphorically.