This is a tough question to answer because there have been so many series and I think you'd have to ask at what point did EACH series jump.
TOS: It never jumped. The stinky episodes are mixed right in with the good ones.
TNG: It would have to be "Unification." I saw the Roddenberry Epitaph on the screen, and not knowing about his death, just turned the TV off. There was no point in going on. Years later I watch parts of Season 7 and I just couldn't get through it, it was awful.
DS9: Didn't watch it, didn't care for it.
VOY: Didn't watch it, didn't care for it.
ENT: Piolet episode. Nothing worked. No chemistry, no feeling, no plot. I suffered through three seasons of it because I had begun posting to this BBS and wanted to join in on the conversation. But that one episode where they showed that alien in a Nazi uniform...well, that was it for me.
MOVIES: "Generations" was it for me. You don't kill Kirk. Sorry, you just don't.
TOS: It never jumped. The stinky episodes are mixed right in with the good ones.
TNG: It would have to be "Unification." I saw the Roddenberry Epitaph on the screen, and not knowing about his death, just turned the TV off. There was no point in going on. Years later I watch parts of Season 7 and I just couldn't get through it, it was awful.
DS9: Didn't watch it, didn't care for it.
VOY: Didn't watch it, didn't care for it.
ENT: Piolet episode. Nothing worked. No chemistry, no feeling, no plot. I suffered through three seasons of it because I had begun posting to this BBS and wanted to join in on the conversation. But that one episode where they showed that alien in a Nazi uniform...well, that was it for me.
MOVIES: "Generations" was it for me. You don't kill Kirk. Sorry, you just don't.
). I knew ENT was merely affirming what VOY had already showed, that Trek had become trash. 
Besides i think people can relate to the simple stuff like that, like, sexual desire and fantasies, bad marriage, getting mad at your family or friends for rediculous reasons and maybe taking advantage of other people's misfortune and make good for yourselves.... You know that kind of thing which draws in the crowd and true to human nature. If anybody say they've never done anything wrong, that kindda crap, they are lying! [laugh] Do think Picard can get all that he really need from Star Fleet rather than real women?! [laugh] he must uses a lot of holodeck...everday! [laugh] Capt. privilege...?