[King of Snake]

It all depends on the type of sci-fi you're talking about. Stories that may rely heavily on predictions of future technology or (indirect) references to world affairs of the period the story was written in may become easily dated. My favourite sci-fi stories, Isaac Asimov's Foundation series and Frank Herbert's Dune series, are almost timeless because they primarily deal with human values and concepts that aren't linked to any particular period while keeping the technology at a minimum (this holds especially true for Dune)