This episode has an old time sci fi feel to it (and a touch of Frankenstein) but is best remembered as "the android episode" or "the episode where Sherry Jackson is wearing that incredible outfit"
Most of the episode takes place on a planet, beneath the surface, with five characters: Kirk and Nurse Chapel (Majel Barrett) from the Enterprise, and Dr. Roger Korby the genius (Michael Strong), Ruk the scary android (Ted Cassidy, . Lurtz), Andrea the megahot android (Sherry Jackson), and Kirk the evil android (William Shatner). (Yes, another double role for the leading man, though this time because one is our Kirk and the other is a machine, it's more interesting than "The Enemy Within").
If this episode were to be made later in its run, Star Trek would likely add a shipboard story to give Spock, McCoy, and the others more to do; indeed, it would be interesting if Spock were to mount a rescue party and accidentally save the wrong Kirk, with the android "captain" finding ways to avoid a physical from McCoy. As is, Spock appears only briefly and McCoy, Scotty, and Sulu don't appear at all. The focus remains primarily on the planet (with dialogue Gene Roddenberry was literally writing at the last minute, scrambling to finish up Robert Bloch's script during the shoot). Dr. Korby believes androids are great, because they don't have feelings of hate or jealousy whereas Kirk believes they are dangerous because they don't have compassion. Inside this framework, the characters have some nice philosophical debates, with action mixed in as Kirk repeatedly tries to get back to his ship. (There's even a question about existence. If we put our mind into an android body to achieve immortality, is the android still us? Kirk seems to think not).
James Goldstone doesn't cut the same pace here as "Where No Man Has Gone Before", but he keeps the wheels from falling of the wagon, giving the story enough movement (and enough shots of Sherry Jackson) to keep things interesting. Sadly, he doesn't get a third chance to sit in the director's chair (likely because production ran two days over schedule, although Shatner intentionally messing up his kissing scenes with Jackson so he could redo them probably didn't help).
Also, I don't know if I mentioned this, but Shirley Jackson is in this episode, and she's smoking hot. (Nurse Chapel gets a good line in. When Korby asks her if she thinks he could love an android, she says, "Did you?" rather than "Do you?" Her real question is rather clear). Looking beyond Jackson's appearance, she really does give a good performance, giving Andrea a childlike innocence that Brent Spiner would tap into in Star Trek: The Next Generation. (Actually, it's too bad Andrea only makes a one time appearance as opposed to a coming on board the ship as a recurring character. As an android like Data, she'd lend herself to some interesting character moments and stories).
In the end, "Little Girls" is fine early Trek, but Kirk and Nurse Chapel aren't nearly as interesting as Kirk, Spock, and McCoy.
Remastered: With so much of the episode taking place underground, there's little for the CGI experts to do except for the "beauty passes" of the Enterprise in orbit and the planet itself.