It's really not well written, by classical standards. It's very colorful and fun and entertaining. But the story and plot constantly use "deus ex machina". Just try an summarize the actions and plot of the movie, it makes no sense whatsoever. Really the story is garbage, but the characters and adventure still makes it fun.

I think that is a feature of a many modern "web novels" or fan fiction. A sort of liberation of the shackles of good writing. Web novels democratized authorship in a way. We really have far more entertaining authors with much more talent than was made to believe (Tangent: A bit like porn today, now that everybody can do it on their own, from their home without some creepy porn producer, we have far better and more creative porn than ever). Most people are creative and pretty good as amateur writers. They just haven't learned the craft of writing a good story lol (cannot be said about Rowlings though, she should have known better).

Why some things become a hit and others not is an unsolved question. If we could answer that, book publishing and movie studios would work very differently. Don't ascribe to quality which can equally be ascribed to luck or marketing.