As usual, the review is structured from bad to good, so please take the time to read it in its entirety.
The worst aspect is the lack of explanations. Starting with not stating explicitly how the function of the GM is to be handled (although it is hinted at that all players do world-building, and it is stated that moves of the adversary of a PC are to be described/determined by a different player) or using scenes without defining the length or scope of them, down to painting things like the revelations (boons you get as experience) in really broad terms leaving them basically undefined. There is a working game in the book, but there are a lot of details that are not explicitly defined.
The design goal is to be open-ended so that players build their own worlds, but the gaps I am talking about are on the level of game rules, and I think those should be complete, especially if the world is to be build from very few hints.
That lack of explanation is somewhat mitigated by the author being quite responsive to questions. I tried out the reddit community, but there are also other channels of communication available.
An aspect that can be either good or bad for you may be the openness of the setting. We have kind of a fantasy setting, with only three deities defined - and even they are rather vague and in broad strokes and it is hinted at that they can be split into various deities with different detailed outlooks/fields of interest within the basic definition. Beyond that, the book offers some names of creatures and places but does not even define them - is Shardvale a village, a town, a valley or maybe even an entire kingdom? Are banewights undead spirits or some kind of goblinoids? And what can they do? Those are all things the players have to determine, the names are just there as inspiration, save for sample artifacts/items to use in your campaign.
The system is GMless or GMfull as the author called their approach in a related, different product, which means that there is no designated GM, instead giving all players the duty to build the world and narrate the NPCs actions.
It is statless, creating distinction mechanically by having different optional deeds (similar to moves in PbtA games) for the characters as well as their narrative description. Over the course of the campaign, the characters may gain relevations that may give them additional dice for some rolls.
It is a narrative system with a tactical dice mechanism which encourages risk taking especially in the early career of the characters. Should characters persevere, they may eventually reach a point where at least moderate success can be reached without taking additional risks, although each action has at least one additional risk besides the risk of failure. Supporting other player's characters means taking a risk where the other player gets to determine in the end whether your character has to endure that fate.
It is kind of a small dice pool system - for each aspect of the action, you add one die to the pool, then roll the dice and distribute them among the aspects as you see fit, one die per aspect and low results being bad, high being good. So, with a mixed result, you may have to choose between succeeding in your action but suffering some harm, or maybe avoiding that harm at the cost of failing at the action.
Add to this that each character has a quest with an adversary (which may also be an environment or situation) whose behavior is linked to the success or failure of the aim of the characters action and whether the main misfortune of the action comes true (bad news in either of these result in the adversary also doing their thing).
Personally, I find this mechanism (with the rules for additional risks that automatically get attached to a roll) quite elegant. It encourages taking risks to get a greater dice pool, which is bound to lead to stories of great risks and great losses, where the price for success may be steep. Thus, the mechanisms also influence the likely tone of the campaign, as the standard rules make it relatively difficult to get positive additional dice for your rolls instead of those linked to risks.
This multi-dimensional aspect (every die rolled is related to some detail of the situation) also assists in the story telling as the dice do not only tell you about failure or success but also about other mishaps or dangers that are part of the situation. So, you are encouraged to be creative before rolling the dice but also supported and inspired once they are rolled.
On a special note, while the rules are intended for multiplayer usage, I see a lot of potential for solitary play because of that inspirational aspect and the way the rules encourage risk-taking.
All in all, I find this to be a very nice game, although some more explanations and details would have been helpful. In a way, it is an unpolished diamond. If you are looking for a rules-lite tactical narrative game for grim or at least serious fantasy adventuring, I would recommend it - with a sidenote, that in the basic rules, all magic players use are wonders granted by their deities and that deities are an important aspect of the game.
Note that the author also provides supplements, one per game, which are all PWYW, with variant rules or settings. Do note, that because all titles use the same core mechanism, supplements can usually be ported to more or less an extent to other games. Especially the supplement for The Queen Smiles, One Red, actually gives much more aid for new ways of playing Succession than dealing with The Queen Smiles.