A show that is still running does not have a crappy ending (yet).
I actually pretty much don’t watch “long story arc” television shows. And when I do, I only watch those that have already concluded and have a generally loved ending. (Babylon 5 is the most recent example of this type of show that I watched and it has a respectable ending)
Episodic sit-coms and cartoons and such, I watch as they come out live. Doctor Who as well (although that one is fading for me). But shows that are essentially long serials like BSG, no, I do not watch as they are coming out. I don’t get into shows like BSG or Lost or Sopranos or whatever because time after time I just hear about people getting burned by shitty endings, I don’t have any desire to set myself up for that. And so far, no disappointments!!
Plus I hate waiting for new episodes. I feel like TV show serials are much better enjoyed when you can sit and watch them quickly. You pick up more on past references, everything is fresher, etc.
BSG and B5 are the only ones of that type I bothered sticking with. I prefer to dip in and out of TNG and TOS with their rounded characters who have moment that might define them, but don’t need to be observed to enjoy other episodes.