Naughty Dog has sliced apart The Last of Us. If you're curious to try Left Behind, the prequel story starring Ellie and her best bud Riley, you can now do that without committing to the larger story (or Factions multiplayer). It's available on PS3 and PS4 as a standalone download for $9.99.
From there, if you do want to upgrade, it's $19.99 for the full single-player campaign and $9.99 for the multiplayer. I fully intend to play Left Behind eventually, but it's hard to commit when Kyle and Darren keep pulling me back into Factions. Such a captivating, time-melting mode.