Ironsworn feels like the natural evolution of ideas presented in Powered by the Apocalypse and Forged in the Dark games. It takes what makes Apocalypse World and Blades in the Dark, and the innumerable games that they have inspired, and further refines their philosophy of play and design.
Ironsworn learns a lot from its predecessors, both in terms of overall design but also in terms of how to explain the intent of that design, and how to play the game effectively. Its simple, approachable mechanics are wonderful and quick to pick up, but the better part of Ironsworn's design is how explicitly it explains those mechanics to you. "Moves" are more clearly defined than in the PbtA and FitD games, as are the majority of the consequences for failing those moves. And gone are the somewhat vague rulings on how to fill a progress clock (replaced by progress tracks in Ironsworn, which do ultimately serve a different function but operate mechanically similarly).
It's still fiction first, as its predecessors are. But it has done a better job of marrying system and fiction in a way that not a lot of games have, and that alone makes it a standout. Add to the fact that the complete PDF is free to download, and it's an absolute steal, and you're really doing yourself a disservice if you don't at least read the book.
Its simple, evocative assets, its loosely defined by thematically rich setting, and its elegant mechanical design make Ironsworn a must-play for anyone remotely interested in the "rules light" or "story game" genre of tabletop role-playing games.