Stargate

Stargate Universe was sufficiently different from the setting's happy-go-lucky norm (and probably also sufficiently expensive) that it has been cancelled after two seasons, compared to SG-1's... ten? and Atlantis bumbling along for a fair while as well. This is a bit of a surprise because Stargate is one of the most TV-friendly - and RPG-friendly - notions in serialised SF.

As John Tynes explains here, it's a setup where four or so modern people (with optional weirdo PCs) walk through a door from our world out onto another planet. The basics of Star Trek but happening right now. Narnia with P90s. Doctor Who early on when the Doctor wasn't so uber, playing as UNIT but the monsters aren't usually bulletproof.

They have an adventure and go home. Bish-bash-bosh, job done, expand from there to include arcs and Earth-based conspiracy plots and other stuff if you want to but you can run just that for yeeeears.

My direct experience of it comes not from the Tynes d6 version, but initially from the Alderac d20 version, and after the second week of a single firefight another player demanded we go no further without changing system so at my suggestion we moved to the Cinematic Unisystem conversion and it went fine. I also ran it as a PBP, still fine. So, yeah, not quite yeeeears but not a bad showing.