I finished the final Harry Potter book last week. It was ok.
Not great. Pretty good. Maybe.
It, and the previous books in the series as well, fell into the trap that most science fiction and a great deal of fiction in general falls into - internal inconsistency. Science fiction is particularly prone to this sort of downfall because of its basis in the fantastical, but any genre is susceptible.
Here’s how it goes… A science fiction writer creates a new technology / world / universe, etc. Throughout the story, some aspects of this new thing are explained and others are not. And then, usually towards the end, a deus ex machina occurs. The reader suddenly learns a new aspect of the technology / world / universe, etc., which is actually a plot device for the conclusion of the story.
For example, the ending of the Harry Potter book, which I won’t spoil for anyone, had me thinking, “Yeah, right.”
The internal inconsistency ending can work in science fiction because the abilities of this technology / world / universe can be made up as the plot thickens. However technique can quickly cross over into abuse and in my opinion, it has. Just because the reader is asked to suspend their disbelief about spaceships, time travel or magic swords doesn’t mean that anything goes. People are still people, everyone has an agenda.
All writers, not just those playing in the science fiction sandbox, need to focus on character development, human motivation as the rationale behind events, compelling plots, and consistency within a universe. Get those down and the rest won’t be easy, but you’ll be well on your way.