Hearts of Stone, the first actual "expansion"-style add-on for The Witcher 3: Wild Hunt, is difficult to write about, because your interest in it is going to be based entirely on how much you want more Witcher 3. Because as much as any single-player DLC I've played in as long as I can remember, Hearts of Stone is very much more of what the base game is already full of.
In a move that almost felt geared toward me as someone who no longer has a Witcher 3 save, Hearts of Stone can both fold into your existing game or be played completely independently, with a new Geralt pre-leveled to 30 with decent gear to start. The DLC gets things moving quickly, introducing a new set of characters who quickly sweep Geralt into a supernatural feud involving powerful forces and the quintessentially flawed human element that's become a kind of trademark for developer CD Projekt Red.
While the Witcher games have always offered a specific, heavily region-influenced take on fairy tales and monstrous myths, Hearts of Stone starts things off with something even more on-the-nose than usual, with a plot involving wishes gone bad, a cursed prince, doomed love and a man who can't die.
There are hints of much more interesting, off-the-beaten path possibilities in Hearts of Stone
After taking a job to clean up someone else's mess, Geralt realizes he's been set up, made a pawn in something bigger, and, because this is an open-world action adventure, has to do a bunch of stuff for other people to become disentangled. If this sounds familiar, get used to it; Hearts of Stone has a new cast, sure, and almost every character it adds is interesting, worth getting to know, but the game around those characters is exceptional only so far as its predictability.
I've played about five hours of the reportedly 10-12 hours of new content — which includes new side quests and discoverables in addition to the main plot threads — and there's not anything particularly different from the enormous amount of stuff to do that already exists in the main game, aside from a new artisan and crafting options.
Personally, I found this a little disappointing. There are hints of much more interesting, off-the-beaten path possibilities in Hearts of Stone, like assembling a crew for a heist and then, ostensibly, executing it. But once things get rolling, that quest devolves into a little combat and some dialogue prompts, and the characters it assembles are gone in a flash. It's disappointingly perfunctory.
That said, the dialogue and backstory is better than most other open-world games manage, which is sort of The Witcher 3 in a nutshell — a game where the craft and care lavished on its fiction and world-building amount to something more than the sum of its parts.
Here's the thing: There's already an enormous amount of that in The Witcher 3 proper. It's not a game light on content by any definition, and my time with Hearts of Stone doesn't put it near the top of the game's best-of list. If you've absolutely exhausted The Witcher 3 and want more, then Hearts of Stone is definitely that. But most of the way through the story, I don't feel especially compelled to play more.