I'm old school enough to complain about the term "Sci Fi" being used to describe anything other than movies. Which is a sure sign this is going to be one of those curmudgeon posts, isn't it?
Personally I find this chart too cute for its own good, and mostly inaccurate. For example,
The Foundation Trilogy is about history in the same way Astrology is about plotting satellite orbits. The Culture series is in the humour sphere? WTF? It's mostly straight-forward action adventure with some intriguing ideas thrown in. (I'm a big fan, BTW.) Furthermore, recommending
Animal Farm for someone who thinks the "world is bleak enough already" might inspire a suicide or two.
Besides all that, recommending the execrable (and largely plagiarised)
Handmaid's Tale to anyone is doing them a disservice. Not to mention the typical dreck from Heinlein and Stephen King -- possibly the worst best-selling writer ever.
The Sword of Shannara is third-rate poppy-cock. I read it when it came out and remember actually waiting for the second and third books. But I was young and foolish.
Dune was rubbish after the first book -- and only just bearable for that length. And yeah, I know
A Canticle For Leibowitz is well written, but it's only a classic because it was taught in schools that wouldn't dare anything slightly less boring.
The Silmarillion is obviously just sketchy notes alongside the magisterial
Lord of the Rings.
Given the inclusion of these titles in the list, I don't feel any need to seek out the books I haven't read. Besides, SF was the literature of the twentieth-century. It's irrelevant now.
My biggest complaint is that this list is conservative, limited and imagination-challenged... exactly those things SF should not be. Ray Bradbury might deserve a few hits, but give others a chance fer Christ's sake! I also notice an overwhelming bias towards American writers.
I could not countenance a list of essential fiction missing Philip Pullman's
His Dark Materials, Moorcock's
Cornelius Chronicles, Zamyatin's
We, Kate Wilhelm, John Crowley, Steve Erickson, John Wyndham, Keith Roberts, Thomas Disch, James Blish, John Brunner, Brian Aldiss, Christopher Priest, William Burroughs, Evangeline Walton, Jorges Luis Borges, Thomas Pynchon and Julio Cortazar.
Plus every short story from J.G. Ballard and about six more PK Dick entries.