This is going to be a piece of fandom, I'm afraid.
I grew up in my teens with Asimov (Foundation series - the first three), Heinlein (Starship Troopers), Clarke (various). I still remember the yellow-jacketed Gollancz SF collection in my local library in Westbury-on-Trym, Bristol.
To be brutally honest, what works for me is a good plot, characters I can feel some empathy with and can believe in, something military and high-tech, and some completely awe-inspiring ideas. This is a multi-pass filter, and only a few folks get through. Greg Egan's Quarantine and Permutation City are particularly good. Dan Simmons's four Hyperion books are stupendous. Greg Bear's Eon and Eternity are well up in my "best ever" list.
Other people I read are Iain M. Banks for his awesome intelligence as well as literary excellence; Peter F. Hamilton for his well-crafted opera; Neal Stephenson of course, even for his baroque cycle :-) ; Paul J. McAuley for Fairyland; Richard Morgan for his extraordinary grasp of low-life ultra-violence in Altered Carbon and its sequels. I really rated Mindbridge by Joe Haldeman, and of course the first two or three of the Ender books by Orson Scott Card.
