I have returned to reading science fiction after overdosing as a precocious teen. I am startled to find how good it has become. I can say without question that the most imaginative and all-encompassing vision of space-faring sci-fi has come from Iain M. Banks. His Culture series of novels pose a galaxy that I find realistic and puts all other post-scarcity novels to shame. Start with Consider Phlebas. You won't be able to put it down, and you will be spoiled for all sci-fi yet to come. I won't tell you what Banks does, but once you read him every other sci-fi will sound lightweight and incomplete. Banks answers *all* the questions of humanity's relationship to the galaxy and once you've finished, you just wonder why nobody else has gotten so far.
The most well-written, ethically thoughtful science fiction I have ever read is the work of Gene Wolfe's Tales of the New Sun. While I'm guessing you mean sword and sorcery as fantasy as opposed to spaceships and high tech, I'm going to say that this is science fiction. It is something else though, it is a deep rumination, told from the first person, about power, and it is told at a distance from a technical explanation about the science involved, much of which is alien and inexplicable. It is in the end a human fiction, a man's long journey into becoming legend through many travels and adventures in a strange land (that may be Earth) but billions of years into the future. It is about the conflicts on a planet of many races that live with a mix of tribal and medieval kingdoms - a planet whose sun has been dying and has lost its ability and knowledge of space travel, and a man whose story is wrapped up in growing conflicts as he gathers mysterious powers. Nothing shiny though. Way better than LoTR.
Then this wouldn't be complete without Charles Stross, who is the single most brilliantly twisted mind in the world of sci-fi. The Laundry Series is great near future, spy-thriller involving a guy named Bob who is a computational demonologist on a hapless mission to save earth from gibbering horrors in other dimensions. But the other works of Stross are great because he envisions the universe as a can of hideous worms in which humans are amusing in their struggles. It really opens up your mind and pours sludge in.
My other favorites are:
Alastair Reynolds : Peter F. Hamilton : Paolo Bagigalupi