Couple of points in defense of the stargate sequence:

a) It’s meant to be seen and heard on what even today would be a pretty insane cinematic setup. Even moreso than the rest of the film, it loses a lot in the translation to the home theater, or even a typical multiplex. Maybe this is heretical, but I’d love to see a carefully upscaled, remixed 2001 in IMAX.

b) The stargate is perhaps the singular element of the film that was the easiest to imitate, vs. say the incredibly thoughtful and detailed production design. So it was replicated to the point of psychedelic cliché.

Genuinely curious if contemporary audiences found it overlong or just perplexing.

I recently did a rewatch where I replaced the audio in 'Jupiter and Beyond the Infinite' with Pink Floyd's 'Echoes'. It really changed the experience for me. Going into 20+ minutes of psychedelic rock after over 100 minutes of classical music really made it feel like a transformative experience.