Cinema Blend says:
Star Trek: The Animated Series was a strange experiment in bringing more adult-themed adventure programming in the animated world, back when it happened in the early 70s. You might assume it was the result of someone who didn’t understand Star Trek thinking that it was kids stuff, but somehow the animated series avoided being a totally dumbed down version of the show. It was an interesting, side trip into the Trek universe at a time when there was no actual live action Star Trek out there for fans to consume. A time a lot like now.