Jean, I'm not fond of the horror/scarey type books whether SciFi or other fiction. I put Something Wicked in with Stephen King's works, not SciFi as far as I am concerned.
Anyhow, if you liked Fahrenheit 451, you may like to try Elizabeth Moon's
Remnant Population. It is about an older woman colonist who purposely avoids being evacuated from a colony planet. She is the only human left there, so she has to learn to do for herself. She begins to interact with the native population of beings that are just beginning to develop skills and abilities as thinking beings. Ursula Le Guin wrote several books which include various moral, political and philosophical issues. We read
The Left Hand of Darkness as a discussion a while back.
http://seniorlearn.org/forum/index.php?topic=1645.0 The Dispossessed , is a bit more dreary and depressing, I think. Both won Nebula and Hugo Awards. I also liked Heinlein's
The Moon is a Harsh Mistress which is about the Moon colony's struggle to become independent of Earth's rule. Jack McDevitt's
Ancient Shores, Eternity Road, and
Infinity Beach are also very good. Regarding Frank Herbert's Dune series, I've only read the first book. It encompasses drama on a dynastic scale, lot's of political maneuvering assassination plots, and has a metaphysical element to it. If you saw the first movie, I think it emphasizes the metaphysical while the later TV movie emphasizes the political maneuverings.
I don't generally care for the fantasy side of SciFi, but there are several here that are. Maybe they can suggest a few titles in that area.
PatH brought up humor in SciFi. John Scalzi comes immediately to mind.
Agent to the Stars, RedShirts, and
Fuzzy Nation are particularly funny. For shear silliness and fun, Douglas's
Hitchiker's Guide to the Galaxy fits the bill.
Pat and I both like the military SciFi. For those that like that kind of thing, Jack Campbell's Lost Fleet series is about the best as far as I am concerned.
Oh, and another favorite of mine is Jack Campbell who writes a series about an antiquities dealer (Alex Benedict) and his assistant which I would characterizes as space adventure. They find and sell antiquities while trying to stay on the good side of the archeological academics and museums. Lots of mystery, danger, detective work and the odd murder or two set in a space environment.
Lastly, I can't not mention Arthur C. Clark and Isaac Asimov. Both have written a wide range of SciFi stories that hit on lots of topics. Grab a book of two of their short stories and pick through them. The same for Bradbury.
BTW, I trust you had a good time here last week. Did your son do well in the race?