Extinction was actually the last straw that made me quit when it first aired.
My God, I'm trying to conjure up positive memories of the first two seasons, all I can remember:
-Hoshi is able to figure out an entire language based on hearing it briefly.
-Hoshi is afraid of transporters -- this leads to random reset button ep that is a hack of Next Phase
-T'Pol teaches a colony of people to defend themselves against klingons by ducking then rolling
-Phlox cures borg assimilation in five minutes
-T'Pol gets a mindmeld transmitted disease and Vulcans don't want to cure it because mindmelds are bad OMG SOCIAL RELEVANCE HOMOSEXUALITY holy fucking shit that is stupid
-Reed thinks saying 'Stinky' to T'Pol is sexual
-Phlox invents the prime directive in five minutes by allowing millions to die for no reason
-Ridiculous time travel storylines
-Trip can't sleep, Phlox prescribes erotic massages from T'Pol
-Porthos pees on a tree, this leads to a revelation that Phlox cleans his long tongue with a metal rod.
-T'Pol likes Jazz
-Alien uses stomach acid to cauterize Trip's wound
-Mine goes through leg
Single scenes, mostly. Every NPC in the first two seasons was written terribly, every story was disposable, and all the emotions any character displayed before mid-season 3 was disposable sitcom emotions.