I didn't like TNG while I was growing up, but whenever I watched the series on lazy afternoons I sort of appreciated that it took things more seriously than the original series.
TOS was comical at best, but since it was shot in a different era is more down to the fact it hasn't aged well.
DS9 was awful IMO, I didn't like that they tried to re-attract the TNG fans by bringing Worf and Chief O'Brien into it. It was far too NATO-esque and political for my liking, and not nearly enough exploration.
Voyager was a vast improvement (especially when Jeri Ryan came into the fold...), with an interesting underlying storyline, and more emotive crew. Chakotay being wary of overstepping a woman Cap, Tom Paris being the reincarnation of serial woman/alieniser Captain Kirk, women in charge of the bridge and engineering was a very radical change. (Being an engineer myself I welcome women to the profession, [SEXIST]especially the good-looking ones

[/SEXIST])
But as mentioned before, the series finale was VERY disappointing. Its like Star Wars ending with Luke waking up from a dream about destroying Darth Vader.