TSFS was excellent because
of the crew interaction. It really highlighted their history and devotion to each other. Furthermore, it was the first time in the Trek universe that we really got a glimpse of our heroes out of uniform. Kirk has a condo. He has hobbies (collecting guns). McCoy goes to bars. etc.... They're people just like us. That (literally) brought TOS down to Earth in a similar way that "Family" did for TNG, and ST09 did retrospectively.