I'm not playing Star Trek Online, but I have been following Tipa's descriptions of the weekly episodes that the STO Live team is putting out. Each week they put out a new short quest line. The story arc completes over several weeks and then a new arc starts.
I thought it was a really good idea, because it fits in beautifully with the source material. Star Trek was an episodic TV show that aired weekly, and mimicking that structure has a certain resonance. What they are doing just feels very Star Trek-y to me, as an outside observer.
And of course, it gives you incentive to subscribe, to "tune in" every week to see the new episode.
Tangentially, before this, Star Trek Online always seemed like the design inherited from the wrong games to me. Inheriting design from DikuMUD style-RPGs like EQ and WoW, with destroyed enemies dropping loot and gaining levels and ships never seemed to quite match the feel of the televsion show. I remember seeing that you could buy and sell officers on the auction house/marketplace, and--green-skinned Orion slave girls aside--that felt really out of place in the Start Trek universe.
I've always thought that the better games for STO design to have inherited from would have the Sims games. Focusing on your officers, and giving them needs and desires, and then balancing that against the various adventures you go on, might have fit the IP a bit better.