For me it's always been more important that Trek have compelling, well-written characters than "big ideas" or deep social relevance.
I actually thought it was the other way around....characters are important but not as much as the others...TOS's weren't as remotely developed as the other ST series..
RAMA
No they weren't quite as developed, but they still came across as dynamic, compelling and real characters (with interesting, well-written dialogue).
Granted, that may have only been Kirk, Spock, and McCoy, but that's more than we got in VOY and ENT.
At least that's the main draw for me, and the reason I rewatch those series more than any other-- for those great little character moments.