Just finished the DLC in one play, played on survivor (which was hard - I died about 20 times in some segments) overall took me about 3 hours. I was really looking forward to this - but looking back, I feel disappointed.
I gotta say while I really enjoyed TLOU, I felt Left Behind was a bit unnecessary and pointless. The whole part with getting the supplies for Joel felt like filler (in a 3 hours DLC!?) and just some excuse to insert action in between the goofing around with Ellie and her friend. It also gave ND a chance to reuse some of it's assets from the full game, so I guess it made for cheaper development.
I was surprised to see it ended when it did, as I was expecting to see something other than
I figured a better ending and a better DLC entirely would to be cut out the Joel fetch quest and have the infection towards halfway in the story. In TLOU Ellie says something along the lines of: "go out all poetic and shit, lose our minds together you know" - I thought that this DLC would follow Rileys demise and how Ellie is the one Left Behind time after time again, after being bitten they continue to live on, (like Ellie's mother said to in her note) to make it out further to see the world with the little time they have left. I would have liked to see Riley fighting both the infected outside and within herself.. and Ellie's journey back to the Quarantine zone when she realizes she's not getting sick - which would be a nice tie into TLOU.
On the positive, the voice acting and mocap are top notch. The graphics (aside from some rough looking water) were fantastic - ND really know how to push the PS3.
Gameplay wise, it was fine, the humans vs infected was fun - but even on survivor I found it way too easy.. just throw in a bottle, let them fight and kill the each other - then pick off the leftovers (try to edge it towards humans, as they don't require headshots and aren't one hit kill).
I felt like it was a missed opportunity for a pricey DLC.
As a side note I don't really care for the facebook stuff, it was cute but a bit distracting.