I came to the manga from the anime. This is important because the anime covers the arcs of the manga that take place in the orphanage. There is a clear split in the reader base in regards to which part of the manga is actually good. That will also affect how you view the anime. In my opinion the anime handles a lot (but not all) of the manga material far better. It's also blessed in that you don't have to deal with every inane, absolutely god forsaken plot point that comes after the orphanage escape arc.

The arcs in the orphanage are a tight, albeit flawed thriller. The characters are constantly using their wits against each other, and for once the antagonists are just as good as the protagonists. It's like the good part of Death Note for dozens of chapters. On top of that the world is interesting and mysterious, truly fascinating. The character designs are incredibly bland, with Ray frequently looking like Sasuke, but I found myself actually caring about these kids as the manga went on.

Then they leave the orphanage, and it goes downhill. Soon no one thinks about anything. The solution to problems becomes guns. There are some chapters that are just actual gun fights between adults, in the military. The plot becomes typical of the shounen genre in every possible respect. The manga goes through the same godawful transformation that Gantz, Dolly Kill Kill, Magical Girl Apocalypse, and countless others do.

This is why some people prefer the later stages of the manga. It's easier to follow, it's more familiar, it's far less ethically uncomfortable. No longer do people have to worry about if they need to sacrifice one of themselves to be eaten alive for the plan to continue and maybe work. Sacrifices are done heroically, in a hail of gunfire, when the cast grows too big. The horror leaves the manga completely.

What's worse is that the manga begins to lean hard on some of the weaker points in the writing that have been there since the beginning. Often times in the early stages of the manga, characters seem to teleport away from an area. Considering they're super humans more or less, it really doesn't seem totally implausible that they could run long distances in a short period. By the time you get to the middle of the manga, people are surviving things that they outright have no business surviving. Normal humans surviving explosions that take out entire bases just for some extra scenes. It's impossible to take seriously, because nothing means anything. Nothing that happens matters.

Early-mid stage manga had issues inserting past events in at random. It resulted in a 'Emma says something happened' and that's the resolution. Even when it's literally impossible that this happened. You kind of take it with a grain of salt however. By the mid-late stage of the manga everything is solved, or taken care of with a time skip and then Emma relays to you that something happened. That's the other problem solving strategy besides guns, cutaways and flashbacks.

Ultimately the obvious human conspiracy plot, the increasing levels of super powers in the main casts, telegraphed character revivals, side switches, and bland world become routine. You can't even say that they're done better than other manga, because they aren't. The art is also not particularly good most of the time, the character designs are weak, the writing dies.

It's clear in a lot of shounen and shounen-adjacent works like Naruto and Attack on Titan that the author planned out the initial arcs, and then just had an idea of where to go from there. And when they got there their ability to ad lib wasn't very good, and they likely changed some plot points entirely. The idea Norman, Emma, and Ray were being saved for a special feast is repeated constantly in the original few arcs, but is clearly impossible by the end of the Orphanage saga, let alone 110 chapters in.

This manga really coasted for me on the first 30 odd chapters. I would say if you want to, watch the anime then never touch anything else. The anime has its flaws, but overall presents everything far better than the manga and on top of that it doesn't carry on after. If you still want to read the manga after watching the anime, be warned that if something annoyed you in the anime it will be 100 times worse in the manga.