Well let's begin.

The promised Neverland has the potential of becoming an extremely popular series. Even though I doubt it could be as popular as One Piece it will probably enter the classics like Death Note.

It all depends on one factor, the length.(Considering the quality is consistent) If it is going to be a lengthy series it might be the next Jump King if it's shorter it would end up being the same as Death Note popularity wise.

There is also an external factor, the anime. If it gets a good anime like MHA then it will become extremely popular.

This manga is original because it's fresh in the manga world. You can clearly see some inspiration of this series with the Movie Chicken Run. Heck, even Isabella is in both. Don't miss-quote me, TPN is not a rip off of Chicken Run but we can see some similarities.

What is interesting is that TPN is another confirmation of the rule: To make great manga, one must take influence outside manga/anime.

JOJO and DBZ weren't inspired by other manga before them, they were outsiders. Toriyama took inspiration of Jackie chan's movies for Dragon Ball and Hirohiko Araki took inspiration from culture and fashion from different par of the world for his manga JOJO.

Those mangas revolutionized the manga world and I expect TPN to have the same influence.

We can even draw more parrallels with Dragon Ball and JOJO both having extremely unconventional artstyle. In TPN's case it is the character design that are that much atypical but the world around them illustrated with an unique style.

So now we have 2 clues that can let us try predicting the series success :
1. Original story inspired by nothing in the manga medium
2. Atypical Art style

TPN have the pleasure to present use with 3 likeable characters that are immediately recognizable and that would make great figurines. It also has appealing cover art making it possibly more likely to achieve success by intriguing the masses.

Anyway that wasn't much of a review of the product but more about trying to identify it's possible success.
Hope you enjoyed.

See ya... English is not my mother language too, so sorry for any potential grammar or spelling mistakes.