It's like a giant pile of plotholes the author never bothers to fix. I thought it was specific to a few works, but upon reading more, I think they're all sorta like this.
He has great early characterization, really draws you in. Then he messes with the reader for 90% of the book, leaving dangling points/characters/etc everywhere. Then virtually everyone dies at the end and the situation is resolved by some Deus Ex Machina. Just about every time.
It's horrifying. I could give examples of this, but I feel it's much harder to find cases where this DOESN'T happen. Off the top of my head, Twins, Sword/Exquisiteness, Flower Guarding Bell, most books in the Dagger series, the Full Moon series, etc. The first 3 in particular have some of the stupidest endings I've ever read (in fact, the second 2/3rds of each book seems to veer further and further from any sense of rationality).
There's SO many extraneous characters that get LENGTHY 1page+ backstories and introduced throughout each novel. Then they either vanish only to be killed ignominiously in a single move later, never show up again EVER (just forgot about them), or die in a big melee somewhere along the way. It's as if Gu Long just started writing, gave up midway, and BSed the ending to his books.
I can see now why Jin Yong is regarded as a far superior WRITER. His stories are 'complete' and things don't just happen for the sake of happening.