Yup. It's a welcome addition to a too-short game.
It adds another interesting story line and some interesting characters, along with some new, even nastier Machines.
The game
really needs more side quests, so The Frozen Wilds is a very welcome addition. (Also, you can get some really good weapons with The Frozen Wilds.)
Also, if you haven't done so,
collect those power cores! If you get all of them, you can use them to get the Shield Weaver Armor, which is awesome. With it, Aloy is virtually immune to attack -- for a short while.
And if you don't get a bit misty-eyed at the end, when you're defending Meridian -- when you're informed that lots of people came to help not for money (shards) or to defend Meridian per se, but because of Aloy -- then something's definitely wrong. To see how Aloy has gone from being despised by her own people for something that most-definitely was not her fault to being revered throughout the land is heart-warming indeed.