Excellent article. I agree the decision not to show the aliens (whether a result of budgetary restrictions or not) is a stroke of genius. That way, the audience can decide whether it is aliens, God, all in David Bowman's head, or something else entirely.

My interpretation re: HAL - I believe as they approached Jupiter, HAL's consciousness came into contact with the monolith and evolved (just as the ape did), hence his murderous attempt at self-preservation. AI itself could have been about to take a leap up the evolutionary chain, rather than mankind. A terrifying thought, which is why the "Daisy" scene remains one of the most disturbing in cinema history.

2001: A Space Odyssey is a singular cinematic landmark; the greatest science fiction film ever made, and I will brook no argument with that. Alas, I fear we will never see its like again.