Both BSG and Lost had amazing first seasons, but mirroring each other, with the second season they both got worse and worse. Of course I kept watching hoping for them to get back on track. But they didn't, in my opinion of course, so I quit them at the time because I just had enough. I still have no great desire to see how Lost ended really. I read something about it, but just posts here and there...
Not sure why I came back eventually to BSG, must be Baltar, I just loved him. And yeah, it ended crappy.
You're right, they were good enough, but after their first seasons/mini I wanted more, but got less. Similar to The Magicians, on bigger scale (it had an awesome last three minutes of first episode). It's still better than a shower of procedural shite that's still on, that's for sure.