Fantasy and Science Fiction on screen is nearly always awful. Yes, I know - big statement to make - but it's true.
The Lord of the Rings trilogy was OK, but I think it weakened as it went along. Partly that's because the last book has so many threads that it makes it hard to squeeze it all into one film, but the point remains that the first film was good, and the last pretty bad. As for The Hobbit, I'm with the majority who say the films are too flabby, too long-winded and, above all, too long. Such a slim novel doesn't need 3 whole movies.
Sci-Fi films usually promise a lot and fall short. There are so many like that - I, Robot; Ender's Game, and Mission to Mars are all good examples. Sci-Fi has always been event-driven, rather than built around characters, but there have to be engaging people in the story as well. When a novel is filmed it too often loses whatever empathy the story had in print, and the film makers replace it with extra explosions. So what we get is stock characters rushing from one near-miss to another, and not much else.
(This means YOU, Desolation of Smaug. Oh yes. Never saw a whole film that was just people running away before.)
TV is no better. Star Trek is self-obsessed by its own idea of human goodness, and most of its aliens are either humans with facial oddities (Klingons, Vulcans) or not carbon life at all (conscious dust clouds, puddles of tar). That's just lazy. Where are the aliens with their own evolutionary history - aliens who are not just from another world but are alien, like the Piggies in Speaker for the Dead or the Traveller Fithp in Footfall? Babylon 5 was just as bad. And Fantasy? Given that I've never seen Game of Thrones - I don't have cable - I can't name a single Fantasy series I liked.
The series I do like all seem to be cancelled after one run - like Space: Above and Beyond and Defying Gravity, both of which were excellent. It's no coincidence that both featured aliens who we humans simply did not understand, either in motive or behaviour. The films I like are forgotten - astonishingly, Silent Running isn't even available online, as far as I can find. How can tripe like Star Wars or Battlestar Galactica endure, spawning new series and films as they go, while quality vanishes so fast?
Simple. Viewers don't like it.
That's a hard truth, because it means that those of us who want to take a reader or viewer into another world are in a quandary. If the public won't watch thought-provoking F/SF on screen for a few hours, they're not going to devote days to reading that sort of novel. So we can write it, but very few people will read it, which makes the process a bit of a waste of time. I want to make people think, but I can write the most insightful Fantasy novel in history and it won't matter a jot if nobody buys it.
So we have to balance the two things. Write something new enough to feel fresh, but familiar enough to feel safe. I'm trying to work out a way to do that, in a story which combines old Fantasy memes with things never seen before, but it's pretty tricky.
Wish me luck.