The Andromeda Strain (the proper 1971 version). Probably my all-time favourite film - science fiction with a story lead by the science, complete with aliens and lasers and microscopes and atom boms and timesharing computer systems and authentic 60s lab equipment and frustrating engineering cockups. All it needs is a better Bechdel score.
Yebbut the science is crap, and as an MD Crichton knew it.
It's good by Crichton standards (and mostly falls under the SF rule of one fantastical element being okay, more than one isn't). And this is Hollywood, it's a good day if gravity is portrayed consistently, let alone the scientific method.
I also like it as an illustration of the late-60s computing Zeitgeist: TTYs were the order of the day, except when using exotic vector displays, clunky one-button-per-thing user interfaces and lightpens. Fluent speech-to-text was considered to be just around the corner, but voice prompts are recordings. They have an automated system for measuring growth of cultures, and can image-process the output of the electron microscope in realtime, but at first resort to manual inspection to analyse the results. As a child of the 80s, it's easy to overlook the technology they got right, and giggle at the whole-room glovebox and be shocked by the blatant portrayal of animal experimentation.
Also, and let's not overlook the value of this: at no point does anyone have a car chase, fistfight, or end up shagging Dr Stone.
I can think of a lot of stories that would benefit from being sent back to the 70s and given the same treatment.