Over the past years we've seen a sore lack of good Sci-Fi on TV.
Instead we were given the likes of
Now all of these shows have very interesting premises that are actually quite engaging. However they all fall short in terms of drama and suspense. And that's what really defines good TV. I think a big reason for that is because they make teenage drama a central part of their plot, which wouldn't be so bad if done properly, but somehow always falls short. Their attempts at family appeal also ruin what could have been a great franchise.
Looking at more successful Sci-Fi, BSG is the best example of how a grown-up approach to Sci-Fi can yield good results.
Blaming it on teenage drama may be a little simple as budget constraints and reliance on CGI are equally important. But I feel that teenagers are just such a huge turn off in Sci-Fi, because they're angsty, behave irrationally and are mostly annoying that I can't recall an example of them being well done.