Star Trek was the only reasonably good sci-fi in the 1960s, but I agree with you that there was a dry spell before good sci-fi started making an appearance in the late 1970s and 1980s.
Edit to add 1969's 2001 A Space Odessy is considered a cinematic masterpiece.
Kubrick was always good for realistic filming. It was particularly difficult during the 'prehistory' section of the movie.
In my opinion, though, that portion took too long. It was a full 20 minutes before switching to the Moon transit.
Kubrick didn't depend on CGI much. It was generally all mechanical effects...some of them brilliantly conceived.
The trip through the Stargate was kinda lame though.
Arthur C Clark's book only went to Saturn, using Jupiter as an acceleration medium. Kubrick shortened the film by going only to Jupiter.
The original Star Trek series was a bit uneven, but had some good writers. One of Gene Roddenberry's biggest job was to keep these wacky writers in line. By the 2nd season, it finally mellowed into a cohesive series. The networks killed it because the want pablum. Star Trek only had 2 1/2 years of its 'five year mission'.
Firefly suffered even worse. It was cancelled by the network for the same reason before season 1 even completed. Despite it's short life, the episodes had formed a cohesive group and they were well written.
Of course, every one of them created some phrases that people repeated often:
"He dead, Jim" -- Star Trek
"It's life, Jim, but not as we know it" -- Star Trek
"One micron and closing!" -- Battlestar Galactica
"Open the pod bay doors, HAL" -- 2001
"My god...it's full of stars!" -- 2001 (now used by some pyrotechnicians when building shells)
"Hey...Bomb...??" -- Dark Star
"Ahhhh, I don't wanna feed the alien!" -- Dark Star
"May the Force be with you!" -- Star Wars
"It's always good to have a blaster at your side, kid!" -- Star Wars
"Welcome...to the real world." -- The Matrix
"Guns...lots of guns! -- The Matrix