Shadows of Esteren: Book 0 - Prologue exists in the liminal space between a quickstart and a starter set. It aims to introduce the game's setting and basic mechanics, offers a selection of pre-made characters in lieu of character creation rules, and concludes with a trio of adventures.
Shadows of Esteren bills itself as "a medieval role-playing game with a horrific and gothic influence." The game's setting is a peninsula called Tri-Kazel that is comprised of three kingdoms. The overall feel of the kingdoms is Celtic medievalism. The lands are feudal and isolated, but they're also experiencing a time of anxious flux; the ancient Demorthen religion (akin to fantasy druidicism) is being contested by missionaries from a Christian analog and by Magience (a kind of proto-Enlightenment scientific revolution). These themes map pretty nicely to Gothic tropes; it sets up a tension between reason (Magience) and faith (the Temple and Demortehn), as well as between tradition (Demorthen) and more modern ideologies (the Temple and Magience). The people of Tri-Kazel also live with the threat of the Feondas--unfathomable monsters who have preyed upon them since time immemorial. The information on the setting in this section of the book is presented in broad strokes, but combined with the more specific information that comes with the scenarios in the back of the book it should be enough to convey enough of the setting's feel to get by for a number of sessions.
The book's explanation of the game system is more akin to a brief summary than a full tutorial; the purpose of this chapter is to give you enough to play the included scenarios. As the text notes, some more complicated areas of the full rules (such as the game's combat and sanity systems) are presented here in a stripped-down form, while other rule systems (such as magic) are omitted entirely. Characters in Shadows of Esteren aren't defined by the usual mental and physical ability scores; extraordinary strength or intelligence, for example, are handled as Advantages and Disadvantages. Characters are instead defined by traits called Ways that determine their personalities and psychological makeup: Combativeness, Creativity, Empathy, Reason, and Conviction. Characters also have a number of broadly-defined skills called Domains. The names of these skills are sometimes a bit opaque; the applications of "Close Combat" and "Erudition" are clear enough, but you might want to have a cheat-sheet handy for what "Relation" and "Natural Environment" cover. Disciplines function like skill specializations, allowing characters to transcend the cap on skill ratings in narrower areas of expertise. What Domains and Ways can be used for is open to interpretation at the table. The task resolution mechanic is similarly loose: players roll a d10 and add the ratings in a Domain and Way that seem applicable to the situation and hope to beat a target number based on the task's difficulty.
Interestingly, the game seems a bit ambivalent about being a game. For example, an aside notes that it's more important for players to role-play well than to game the rules, and that they should "limit the use of the game system to a minimum" (17). Clearly, the system has been kept simple so that it can remain "off-stage" until needed to resolve some bit of narrative tension that can't be decided based on role-playing alone.
The six pre-made characters are far more than just filled-out character sheets. Each characters gets a full-page portrait, a hefty block or two of background text, and a description of the character's personality, along with all the pertinent stats. The characters' back-stories help fill in the broad setting overview given at the start of the book; through those backstories we learn of the Varigals (professional news-bringers that travel the Tri-Kazel), the order of Hilderins (a knightly organization), and the religion of the Temple.
The three scenarios in the book are tied together but can be played in any order. The book suggests two different sequences to chain them into a short campaign. All three scenarios are largely investigative: "Loch Varn" involves navigating a series of flashbacks to figure out how the characters got to the place they awaken at, "Poison" casts the characters as detectives looking for the cause of a poisoned river, and "Red Fall" has an amnesiac adventurer waking up with a bloody sword and a half-eaten corpse beside them. Each adventure is heavy on text and will likely take some time to prepare, but the use of helpful icons to guide the GM's way are a nice touch.
As an entryway into the Shadows of Esteren series, I really don't see Prologue working for new or inexperienced players. There is simply too much in the book that relies on already knowing some of the ins and outs of role-playing games. Similarly, some of the scenarios in the book would be an absolute nightmare for new GMs to run for their group; "Loch Varn," in particular, has a complicated timeline that is central to pulling the adventure off successfully.
Players and GMs who have already cut their teeth on other games might have a better experience with Prologue. As a physical object, the book is a gorgeous hardback with fantastically moody art. The setting's blend of Celtic, Gothic, and almost steampunk-ish weird science is unique, and the world certainly carries and conveys its own flavor. It's also worth noting that the English version of Shadows of Esteren was translated from the French edition of the game, and frankly it sometimes shows. While the game's often baroque verbiage could be an attempt to capture the Gothic's purple prose, it feels like something is frequently being lost in translation. This is particularly vexing when the language barrier gets in the way of a clear explanation regarding the finer points of the rules. Nevertheless, although some lines might require multiple readings to parse, it is possible to put all the pieces together.
However, Prologue is something of a tease--while there is enough to play a handful of sessions with, you'll definitely need Book 1 - Universe to get the full Shadows of Esteren experience.
Book 0 - Prologue is available as a free pdf here.