I'm asking this mainly of fans who are too young to have watched TOS during its initial run.
The Next Generation premiered when I was six and it quickly became my favorite show. I stuck with the 80s/90s series through to the end of Voyager, and watched Enterprise sporadically. It was not until I was an adult that I watched the Original Series all the way through, and it took me a long time to learn to appreciate it. (Blasphemy, I know.)
If it were not for TNG, I doubt I ever would have given any time to TOS at all, much less grew to love it. Anybody else feel the same way?