A cinematic masterpiece to be sure but certainly not for everyone. As everyone says it looks glorious and that largely holds up in the 21st century. The ideas here may be elusive, particularly upon 1st viewing, but they're impactful especially as we hurdle toward AI influencing everything in our lives. I suggest a companion analysis immediately afterward to make sense of some of it.
If you're looking for something bombastic, you're not going to find it here. This is meditative filmmaking that moves like a slug but that's where the beauty of it lies. The monolith is a brilliant and fascinating take on human evolution and possible alien life. The absence of a culprit who placed it makes it that much more eerily mysterious. The later sequences with HAL, the ship's AI, are unsettling and stick with you.
The purposely mundane characters will bore some, as it did when it was first released but, oddly, that's the point. This all creates an atmosphere that draws you in and puts you off-guard; then suddenly you are blindsided not by some sort of explosion of violence but by something else that isn't easy to define, something that lingers as you contemplate what you've just seen. Not many films can challenge you that way.
This is often compared to Tarkovsky's Solaris. Some say it's Russia's answer to 2001, but Tarkovsky had few admirers in the Soviet nomenklatura. The bureaucracy sensored and ultimately banned much of his work. But, like Solaris, 2001 leaves ample space for subjective interpretation but is definitely more accessible for American audiences. Solaris made me wonder what I was watching and after it was over I couldn't help but think about it. I wasn't sure if I even enjoyed it in the traditional sense. 2001: A Space Odyssey hits similar notes and in that way they feel similar and years later I understand that's a great thing.