Downloadable Content (DLC) has grown by leaps and bounds over the past decade. In its earliest days, it was seen as nothing more than a way to squeeze additional money out of customers who had already paid for the core game. For some, this is still the prevailing opinion on DLC, but there's no denying that the quality of this content has gone up over the past 3-5 years.
DLC has come to include a diversity of releases such as maps, prequel material, epilogues, and additional mid-game content. With Bioshock Infinite: Burial At Sea Episode 2 coming up and the recent release of The Last Of Us: Left Behind, has DLC finally come into its own, or is it still a non-essential experience? For that matter, does it matter in the grand scheme of things one way or the other?
Both of these pieces of DLC show just how malleable the format is, in incredibly different ways. Burial At Sea (which we now now has a deeper context to it's development, with the announcement of Irrational Games shutting down) serves as one final adventure in the world Ken Levine's team has been creating for the better part of ten years. It's a send-off for both the studio and fans of the Bioshock universe. Think of it less of an epilogue, and more of a declaration.
Left Behind, on the other hand, is all about nuance. It's a short tale focusing on Ellie's life prior to the story found in The Last Of Us, and adds context to everything that happens throughout the story.
Neither piece of DLC is nessesary to enjoy the core experience, but both enhance it in meaningful ways. This is the sweet spot DLC should always aim for. DLC that leaves out vital elements from the main game (Prince Of Persia reboot, Deus Ex: Human Revolution, and Mass Effect 3, I'm looking at you) is cheap and crass. DLC that is just more of the same (Assassin's Creed 2's offerings, for example) will only appease the hardest of the hard-core fans.
Enhancing a game's story without taking away from it is where you get truly interesting experiences. It's why Bioshock 2: Minerva's Den, Red Dead Redemption: Undead Nightmare, the Grand Theft Auto IV add-ons, Far Cry 3: Blood Dragon, and Assassin's Ceed IV: Freedom Cry, all seem to be universally praised. They not only offer more stories to explore, but in their own unique ways they all enhance their respective core game's experience.