The Last of Us: Left Behind is made out of two very distinct halves. One that focuses on exploration and combat encounters, while the other one focuses on storytelling. The two are loosely connected both in terms of story and gameplay, which makes the frequent jumps between them a bit jarring. That being said, both halves are excellent and make this DLC well worthwhile.
Pros: The story of Ellie and Riley is excellent, interesting side story during Ellie's solo campaign, superb writing and characters, great environmental storytelling, great atmosphere and attention to detail, overall good combat encounters and rock-solid game design, varied gameplay, nice mix of stealth, combat and exploration
Cons: Two distinct portions intertwine one with another, while barely having any connection between themselves, cumbersome to switch between different weapons in the heat of the moment, a few scripted enemy encounters that come out of nowhere