I realize the thread has moved past this, but I want to resurrect this issue of sticking the landing.
I feel like the harsh realities of TV make it unfair to lean too heavily on how a show ends. You have to get real lucky to have the kind of advance warning needed to put together a true ending, and so many of the best shows aren't ratings hits, and are always wondering when they'll get the axe. Plus, by the time a show ends it might have different showrunners, major cast changes, etc. And also some shows, particularly in the pre-serial era, just sort of end, because there was no central thruline anyway. Cheers had a very cool final scene, but if the show had ended 10 episodes earlier, who'd have cared?
TV shows are too different from movies or novels to really put the same weight on endings, I think. What if the charitable thing to do is to just gauge them based on the overall impact they have on you? For example, I thought the X-Files was the greatest show on TV for a while there (not that TV was particularly great at the time), and once the leads were gone but the show was just shambling along anyway, I was gone and that was fine. Even the ho-hum/bad movies were sort of ancillary to me, and I avoided the revival seasons like my life depended on it.
For someone else, the movies or those last seasons might have retroactively snuffed out any affection for the X-Files. I'm not saying you should always give bad endings or follow-ups a pass. Just that you never know when Deadwood or Rubicon or My So-Called Life or tons of other great shows are going to get cancelled, and that shouldn't automatically knock them out of any halls of fame. If Friday Night Lights had ended a couple seasons earlier I'd still think it's a masterpiece.
I managed to talk about a lot of non-SF shows there, maybe since I think most SF shows aren't all that great. I'm just saying that the upcoming final season of the Expanse could somehow be the dumbest thing possible and I'd still rank it higher than just about anything in the genre (on TV).