Some of the orchestral music is good, but there's a little too much of the standard "weird and eerie 50s scifi music" that Roddenberry was so dead-set against having on TOS.
Nothing intrinsically wrong with that. Roddenberry was trying to do something new and distinct from what had come before; Allen was just trying to do another of his adventure shows.
Besides, a lot of that "eerie '50s scifi music" was tracked from Bernard Herrmann's score to The Day the Earth Stood Still
, and that's one of the great SF film scores of all time.