I think what made DS9 fail for me during the time it originally aired was as others have mentioned, I initially thought the premise sounded boring. But more than that...having watched the entire series now, I really believe another reason the show failed was because the main characters, guest characters, relationships, alien species and ongoing threads became so complex, it was hard to jump in and catch an episode here and there and just enjoy it on its own. TNG was more episodic. This is oversimplifying it and certainly there are exceptions, but in TNG the characters simply weren't as multi-dimensional, so the shows were more about the individual stories than they were about complex character development, recurring guest characters or ongoing threads. I'm not knocking it, because I certainly enjoyed TNG. But by its nature it's much easier to catch random episodes of TNG here and there and know what's going on, skip around and still have the same basic set of defined characters. DS9 on the other hand was always adding characters and threads here and there and bringing them all back, so if you tuned in at random (as I did), you were just completely lost and uninterested. While I found the idea of a space station with shuttlecraft boring, I still tuned in from time to time hoping to love it. It never happened during its original run. But now that I've watched the entire series on Netflix, it's my favorite. Isn't that funny!