DS9 was something of an exception for Star Trek in that it did utilize story arcs to an extent, but Babylon 5 was one continuous arc, and epitomizes space opera. I was, however, responding to JayJay who stated that he did not like the soap opera feel of DS9, and I was just noting that Star Trek in general comes very close to meeting the definition of space opera (a soap opera set in space), but most Star Trek series' do not embrace the defining space opera feature of continuous story arcs.
J. Michael Straczynski, the creator of Babylon 5 has maintained that Paramount actually stole the idea of DS9 from him, as he pitched the idea to them 5 years before either series premiered. He then pitched the show to WB, who announced the development of Babylon 5 a few months before Paramount announced DS9. Paramount did, however, premier DS9 a few months before Babylon 5 premiered, leading many Trekkies to conclude that Babylon 5 ripped off DS9.
And based on my rather neutral position, having loved DS9 when it came out and never even saw Babylon 5 for well over a decade (and see Seasons 2 through 4 beating out DS9 easily (only DS9's really good episodes compare), there is very little in common with the two shows and the idea it was stolen seems silly. The only thing in common is that they both take place on a stationary ship.
This article tackles some of the more recent evidence that supports Straczynski's story, but I think most fans of both series who know about the controversy do accept it as true:
http://www.tor.com/blogs/2013/02/is...-proving-deep-space-nine-ripped-off-babylon-5
I was working at Warner Bros. in the publicity department when Warner Bros. and Paramount were preparing to launch a joint [emphasis mine] network. Warner Bros. already decided to buy Babylon 5 for their adhoc PTEN network (a group of independent stations that agreed to show Warner Bros. shows in prime time.)
Paramount and Warner Bros. both agreed that Deepspace 9 would be the show that would launch the new network and there wouldn’t be room for two “space” shows on the network. I was told they purposely took what they liked from the B5 script and put it in the DS9 script. In fact, there was talk of leaving the B5 script in tact and just setting it the Star Trek universe. I had to keep rewriting press release drafts while they were trying to make the final decision.
But then, suddenly, Paramount decided to launch a new network on their own and screwed Warner Bros. over. That sent Warner Bros. scrambling to create their own network; grabbing up any station not already committed to Paramount and getting WGN to show the WB network on cable.
So Paramount definitely knew about the Babylon 5 script, I don’t know about the DS9 show runners, but I find it hard to believe they didn’t know.
Though Straczynski and WB never pursued any legal action, they likely would have had a fairly strong case.