I'm not a big reader of science fiction, but I love it when it's well done. (Michael Crichton comes to mind.) Good sci-fi writers explore interesting social questions while constructing cool plots about things that haven't happened...yet.
My complaint with SF is that all too often the story ends with "and now we must kill the aliens before they kill us." The last few chapters are the all out battle for the survival of our species, with lots of things blowing up and gallons of green blood spilt.
That's not my thing. In the most recent example I read, the story began well, with questions about how time travel would actually work and what the resulting physical and mental problems might be, but it ended up with monsters pouring out of the portal and lots of shooting. We started with questions and ended with an arcade game.
SF isn't the only predictable genre, which is why genre fiction has a bad name with literary folks. Who hasn't started a romance novel and known from the first chapter what was going to happen and who was going to end up living happily ever after together? (Sometimes it's a tossup between two men, but if you go with the less socially acceptable one, you'll probably get it right.)
Mysteries are often predictable too, and after reading them all my life, I really enjoy finding one that escapes the rules a little. An interesting (but not mean) sleuth is great, a unique setting is nice, and if at all possible, a solution that's clever and even obvious...after I read it. Too often these days I know the "who" early on, and I tend to skip chapters to get to the end and find exactly the same thing that happened in the last five books I read: The protag is bloody but alive, the cop that doubted him/her becomes a friend/lover, etc. etc. etc.
Even "literary fiction" novels, those books that are supposed to "transcend genre," are often the same old same old, and lately they seem to come in streaks. I'm tired of books about bookstore owners who are delightfully fey, tired of titles with "Girl," and tired of lead characters with no redeeming qualities who wallow in their own misery for 400 pages and end up exactly where they began.
If you're nodding your head as you read this, I know what's wrong with you. You have read TOO MUCH. YOU NEED TO STOP READING BOOKS. (YOU NEED TO STOP WATCHING TV AND MOVIES TOO.) YOU NEED TO GET A HOBBY, LIKE COLLECTING SPOONS OR WEAVING YOGA MATS OUT OF OLD GROCERY BAGS.
Or you can keep doing what you're doing, looking for the one book in ten that occupies your mind and satisfies your heart. That's what I intend to do!