I've seen 17 of the films on that list and the ones I haven't are older (Forbidden Planet, Body Snatchers, etc) or ones that I considered horror more than sci-fi (Thing).
Oh man..
The Thing is an absolutely brilliant movie. You should make the time to watch it.
I've seen all but 5:
Forbidden Planet
Brazil
Metropolis
Invasion of the Body Snatchers
The Day the Earth Stood Still
All but Brazil are way older than me, so that's my excuse. I know I saw pieces of
Forbidden Planet and
The Day the Earth Stood Still on TV as a kid, but I don't think that counts.
I've seen
Blade Runner several times, and it never did it for me. Every few years I'll sit down with it thinking "this time maybe I'll get it" - but I never do.
I absolutely LOVED
A Clockwork Orange back in college - enough to actually read the original novel. I don't know if it would resonate with me as much now with me being old and married and a father, but it was a great, inspirational tale of the triumph of individuality back in the day.
A few lame ones in there.
Avatar? Please.
Moon was a darling of critics, but I found it pretty boring outside the premise.
And by any measure
The Fifth Element should be in any Sci-Fi top 25. I'd also add
Predator,
Contact, and if you want to throw in something fun,
Starship Troopers.
