My 13 year olds still watch TOS with me. My daughter dislikes Doomsday (gross, which means she was scared by it when younger). My son has always loved Arena. Tholian Web was a winner. Oddly enough, the Changeling, too, which doesn't seem real kidlike. My daughter really likes Spock and finds him very funny, which he really is. And not in those "3,467.298 to one" odds moments. His character driven retorts and statements are often funny. Way more, to me, than the so-called humor eps.