Really depends on the show. Lost's finale was a little disappointing, but the journey overall was awesome so I'll still rewatch it.

Falling Skies, on the other hand, had such a prolonged descent - four seasons!!! - into an absolute utter shitshow of plot armor and every season throwing out the rules and continuity from the previous ones that it was just an absolute hate-watch to the finish line. Being part of /r/FallingSkies during that time was very interesting, because I'd never seen a fandom so unified in ripping apart a show they'd all previously loved.