Hum, the ending had to be remade after first screenings, and even as-is, it's subject to critique by many, diminishing the value of the entire film. (I recall it even being laughed at. I guess, audiences may have become more tolerant, since.) It may have done better with a more abstract solution, as well.

(There may be specific topics where "show, don't tell" becomes "experience, don't show". And 2001 tried to accomplish this. The Abyss, on the other hand, tried still to show, probably failing in its mission. — There was a time when German media theory, in the wake of F.A. Kittler, was kind of obsessed with the written signifier of the novel giving rise to an immediate, visually representative significant. Observed from this perspective, even Clarke's novel takes a step back into abstraction: we may find it hard to invoke an immediate imaginary representation, while reading, the narrative pretty much falls back to us being told, instead of giving rise to imagination, much until the last, much more "tangible" gesture of the Space Child. But, even then, the perspective of the Space Child, cynical without cynicism, and what may come of this, is very much an open ending. So, why not move this openness forward in the plot?)