Have you ever watched a movie and said “This sucks, the script is horrible, the story is weak and the sequence of the movie is all over the place. The director should be fired”?  Most of the blame should fall on the screenwriter,  the person who wrote the screenplay which determines the flow of the movie or the producer that approved it. (unless of course its the director that goes renegade)
The goal is to finally produce a screenplay the production crew and talent (actors) can visualize the entire move. Writing one is a little different from novels because it expresses in detail every scene that makes up the movie in order. It describes the location, mood, environment, objects, characters and interaction between the characters. Many times it also describes the transitioning between the scenes.
A good screenplay would allow you to visualize the entire movie just by reading it. You can check out one that has been analyzed and commented upon here
The key component of any movie should be a compelling story. Without getting lost in the technicalities, you can opt to write an early script (or adapt from a novel) to outline the overall story, explain the world as you see it, and properly build up the characters.
So what do you need for a good story?
Basically you just need conflict. A hero and a villian like Batman & The Joker or Best friends falling in love with the same girl.
Having a plot would help as well, a series of events to leads to a climax or ultimatum. It could be character development (from zero to hero), or revealing an unknown world and conquering it. The plot works to bring the most out of the protagonist and antagonist (hero and villian) and creates a greater emotional attachment and adds realism to their characters.
The final key is to give an insider view to the interactions of the characters and lay out elements of the plot so that your viewers will be able to deduce the general flow of the plot without being predictable. This allows your viewers to be more immersed with the growth of the story and deeper understanding of what drives the characters to make certain decisions.
Sprinkle on some love, war, unexpected loss and you’re on your way to a brilliant masterpiece.

In that case, most of the failed adaptation from other mediums are due to bad screenplay? Is the screenplay like a guide for the director or do he follow it to the dot.
Usually it depends. The director has the final say how the scene goes. In ideal cases the director should refer back to the screenwriter if there are scenes where the intended storytelling is vague.
Most of the time though, the director will follow the screenplay and decide on the viewing angles and cuts to give it a creative flare.
From what I’ve seen & read, it all depends on the director. He can follow it to the dot, or he can take the screenplay & rewrite whole sections of it if he doesn’t like it. So in the end, blame can be on both.
Thats exactly what u mean by the director going renegade…
However for Storm Warriors.. its like as if the director got his pages clipped in the wrong order
I wouldn’t call it going renegade, since it’s just part of the movie gets rewritten. Sometimes even the actors come in & rewrite the scenes, like what happened in Iron Man. But of course this is rare.
Storm Warriors, I haven’t watched that yet. So you’re saying the story is solid just that the director told it in the wrong order? LOL!
Nah… the story also not really solid… but this one like everything no point one… and order messed up too.