After I wrote the above I went to check the list: I've read about 33 of them (slightly lost count at the end through someone talking to me...

people! Can't live with em, can't live without em!

)
But some of the comments after the list! Someone actually thinks Red Dwarf should be on it... okay, I've not read the books... I enjoyed the tv program but to insist that the novelisations should go on a top 50 of all time?!
And another thing!

I've read 1984 twice, and I reckon it's the most over-rated book I've ever read! It's a simple political allegory, not a flipping great novel of any kind, let alone sf! It's not sfnal in the least! And as to "character"... there's none! Just caricatures of types... there's no humanity, just dregs... how on earth could such a situation ever develop in Britain? It's an allegory of the soviet union, back when people didn't know that Stalin's nightmare had betrayed the vision for which so many intellectuals were proselytising in the capitalist west back then. Sure nowadays we could all be plugged in to pleasure machines without our noticing.... could we? I couldn't, could you? The system buys us more subtly than 1984 ever dreamt, but still we have far more gumption and spark than Orwell's allegory allows.
I figure people still think somehow we stole a march on the literary mafia by sneaking one of "ours" into the Received Canon of the literary world.... but I doubt any of "them" see it as anything but a historical curiosity... I can't see it being called great literature by the people who read modern fiction.... maybe I'm wrong about that, but really, sf has produced so much more literary and truly great writing than
1984,
... if you ask me, Kim Stanley Robinson's Mars Trilogy is far more of a proper novel than Orwell's, and the extended wrangling over the Martian Constitution provided an opportunity to construct a totally devastating critique of laissez faire capitalist american politics, far more effective and true than Orwell's one note symphony. And the same author has provided us with a gripping investigation of american lives and the way science is done, and also besieged with nonscience, in his more recent trilogy
Science in the Capitol, which I truly rate as Great Literature.