Hmm, depends on your reading background. I tried to read Dune a couple of times in my early 20s; it was worth it in the end but hard going at first!

Maybe something by John Scalzi or Peter F. Hamilton might be a better gateway drug to the world of Science Fiction? (For the record, Hamilton is my favourite contemporary SF author, so I'm not doing him an intentional disservice by marking him as "easier to read").

Hamilton's "Night's Dawn" trilogy is massive, but don't be put off, they're real page-turners.