My thought is the ending, so imma spoiler this:
The ending was... interesting.
I do think that Karellan might lead a revolt against the Overmind, since he did say "let's leave [the music] for whomever may come by," and if his specie is simply designed to go out and uplift species, he would have no use to go past Earth again, nor will any other specie if the stars are "not for man," then why would it be for anyone else?