It's about Islam. The monolith is a stand in for Muhammad.

Yeah, it's a human zoo. It's laid out in the novelization, which was written contemporaneously with the film. Kubrick collaborated with Clark on expanding The Sentinel into a full length story. The meaning has been explained since the debut of the film.

that's deeper than what most people gave it. 5 stars.

In the later books, it's implied that the Monoliths are studying humans in order to turn them into sentient computer programs (basically mega-advanced AIs) for purposes that are not entirely clear, though I always assumed the implication is that the Monoliths (or their controllers) eventually wanted to be able to create synthetic beings from scratch, including their whole brains and such, since playing creators and gods was essentially their whole deal.
I honestly thought 3001 was a weak-ish ending for that series, but in retrospect, I'm glad Clarke didn't bother with some ham-fisted climax where we meet the aliens or anything stupid like that. They just remain a mystery and it probably should be that way.