As long as I’ve watched nearly 3 seasons of the Deep Space 9 series of Star-trek, I try to compare it with another series of Star-trek, The Next Generation. Although they both are classical science fictions working on a probe into the space (and human nature in fact), the source material of their storylines are exactly different.
TNG is a standard space exploring series. As it’s about a ship going around the space. It got a platform in freedom space for creative work of storyline. On the other hand, creative platform of DS9 is limited on a fixed Bajoran space station. The main thread is focused on the political issues between Bajor, Cadassia and the Federation. DS9 is quite strong to deal with topics about race conflict and politic but its science fiction smell is not so strong. I personally assume it as a politic story in a science fiction coat.
I still miss the kind of stories of TNG as a classical science fiction.