Eye spotted two reviews for the Witcher 3 Expansion Hearts of Stone:

The Escapist:

The Witcher 3 - Hearts of Stone Review - Storytelling Excellence

Hearts of Stone is CD Projekt Red's first paid expansion for The Witcher 3. Except, it isn't really an "expansion". In gaming, the word expansion conjures up images of huge packs of additional content, that often drastically changes the playstyle, or bring with it an entirely new experience. I think of Heart of the Swarm for Starcraft II, or Throne of Bhaal for Baldur's Gate. Hearts of Stone on the other hand, is best compared to the DLC "episodes" of games like Fallout 3 and Borderlands - a short, self-contained adventure that simply takes place within the original game's world. But please do not take this semantics discussion as a negative, for Hearts of Stone, despite not really being an expansion, is most definitely worth the price of admission. [...]

Bottom Line: Hearts of Stone, despite not really adding that much new "stuff", tells an amazing, engaging story that is worthy of the $10 price tag. While The Wild Hunt was the conclusion to an epic, climactic saga, Hearts of Stone is simply another story in the life of Witcher Geralt.

Recommendation: If you're looking for an expansion of The Wild Hunt, you won't find it here, but if you are just looking for another bite of CD Projekt Red's incredible world-building and character development, then Hearts of Stone is for you.

Score 4.5/5

Polygon:

Witcher 3's first expansion isn't terrible or great, and that's the problem

"Hearts of Stone," the first actual "expansion" style DLC for The Witcher 3, 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 singleplayer DLC release 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 that 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 CDProjekt.

[...]

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.