The sets are repetitive in TOS, I guess I just love how darn colorful and 60s-esque the show was. I also enjoyed it as a look into 60s era world-views and how sci-fi proposed to deal with the then current issues. I think there was an episode that essentially equated to a justification for the Vietnam War lol.
Yeah, I guess I kinda dig the psychedelia hippie thing too, and some plots that really pushed the social boundaries of the time. I'm probably being too harsh
