It was... okay. I found the moments between Ellie and Riley boring, as a game. As a story, it's interesting, but to play it it's not... fun. And what actual parts are gameplay, there's so few of it. The three-way-encounters aren't even anything that special because the way they have them set up it's purposefully done so one side will win if you do alert them. It's cool to see, certainly, but I don't see how the side with less numbers could win out with how the AI works.
I played it on Hard and it wasn't as difficult as it could have been. I maybe died twice and that was because of purely stupid mistakes. Suffice to say, I don't really have any interest in replaying it because of those moments between Ellie and Riley -- they'll get in the way of why I'd want to replay it in the first place.
This probably would've felt better in the main storyline, it really feels like it was planned for the main story but they prioritized other events over it. It was definitely a whole chapter, in terms of comparing the length of it to the chapters in the main game.
Feels kind of cheap they spent like 80% of this DLC on conversation and forcing the player along hallways to do interactables to initiate conversations. I guess it keeps your interest for a bit and I appreciate them showing what their relationship was and showing what kind of person Riley was. But as far as pure gameplay content? It's lacking for something that was $15. And I understand why it's $15 and why much of it is more narrative than gameplay (especially because of the story they wanted to cover) but man it feels really lame because much of the actual gameplay content (the encounters and the time frame these encounters are from) are from a portion the main game that were cut due to time or whatever.
Those are my 2 cents anyway. Not particularly glowing like the rest of you -- I loved the main game, obviously, but this just didn't have enough action oriented gameplay. I don't think it was balanced proportionally as it could have been. And I guess, again, that's because of the story constraints they put themselves into (exploring Ellie/Riley relationship and showing what happened).