From the great acting (from both leads, one which surprised more than the other) with memorable moments and interactions.. to great cinematography and execution of almost every visual element! If you are a fan of the game, it would definitely be worth watching.

BUT.. to anyone not immersed in the playable original story, I would be remiss to recommend it as a stand alone. Partially because it feels rushed in parts, and lacking in others I feel are very centric to what Last of Us is. And certain parts feel too disconnected and separate from the main narrative (I can also see this part annoying some viewers). Still, there's plenty of World building here.. and as the YouTuber "Just Write" so eloquently put it on his short review of the series, it's a show that justifies its existence by turning "subtext into Text", by adding more to it (instead of just being) and providing different point of views to what most of us knew coming in.

What I'm saying, is go play the game if you can.