That's only if you consider, say, a bunch of ten year-olds running around a dining room table while throwing cutlery all over the place "entertaining", while the adults, meanwhile, having a quiet, dignified, and mature conversation around the dinner table is "boring." Sure, TOS, even when terribly written and conceived, seems more "entertaining" because it is colourful and loud and brash and entirely juvenile (when it's bad, I mean.) TNG is quieter, less colourful, less bombastic, more sedate, and more thoughtful - and that may, to some, seem boring, I suppose.
Hell, I'm 35 years old, and I'd rather play with the kids than have boring "adult" conversation!

Maybe I should have said "stately and sedate". Don't get me wrong, I don't mind "stately"...at times. Just a couple of days ago, I re-watched TNG's "The Outcast", and I was thinking that it was a better episode than I remembered. However, sometimes I want my entertainment to be purely entertaining, an escape. I want action and adventure, and TOS, even at it's worst, usually provides that. That's what I appreciate about it the most. It's why it's my favorite, and not that I want to speak for him, it's why I think that Warped9 perfers TOS season 3 over any TNG season.