A lot of folks look at TNG with rose coloured glasses. Don't get me wrong, it was one of my favourite shows growing up. However, it was just as cheesy as Enterprise and TOS at times. Probably more often than not. As for characters, two words, Wesley Crusher. Or pretty much any child actor on the series. They didn't know how to write parts for kids.
TOS is what it is. It was a campy little sci-fi show that got cancelled after two seasons, then revived for a third only after fans bitched. Nobody watches it for insightful drama. They just want to see Kirk beat up men in rubber lizard suits.
I enjoyed both Enterprise and Voyager. Both are underrated IMO. Didn't care for DS9. Tried to take Trek in too gritty a direction.