IMO, Robocop is better today than when it was made. I honestly didn't remember that movie being so good. I guess I was too young to appreciate it, and though it was just an action movie.
The only thing I remember about Robocop (I saw it when I was around 6), was someone melting because they were immersed in toxic waste (I think). That was f'ing awesome.
We had a discussion at work about that scene a few weeks ago. I haven't seen the movie since it came out with the exception of that scene. That scene still holds up.
Anyrate, bladerunner, the Thing, Dark City, aliens, the original The Day the Earth Stood Still, all hold up. I only just realized, I've never actually seen the original Alien. Clock work orange still works for me and I never liked 2001.
When I think about older Pre 1980 sci-fi, its hard to come up with more than a half dozen examples that aren't B-movie crap. That may be why they don't seem to hold up so well, they were the equivalent of a SyFy original production.
Not exactly Scifi but yeah, NxNW still works as do a lot of Hitchcocks stuff. If I liked it in the first place but he and Kubrick are hit and miss for me.
Can't help but notice that nobody has mentioned star wars or star trek yet.