Thanks for the inquiry!
Previous editions of WFRP suffered from serious issues with skill distributions between specific lines of careers. It created lopsided career paths that severely impacted the way percentile math worked. While on the surface, two careers deep did little to upset the inherent balance. But once you got three+ careers in, you could visibly see the cracks. Couple that with an unbalanced distribution model of talents and advance bumps, and the game became a mathematical nightmare where you had players who were four careers deep, but didn't have an even, fair distribution of skills, advances and talents between them.
ZWEIHÄNDER introduces a "fairer" model, creating an even distribution of skills, talents and bonus advances over each profession. Additionally, it creates a broader path model by archetype. This means that every archetype has 13 nested professions below it, which models the old career paths but allows people to move between archetypes without unhinging the skill distributions. It is a far more elegant solution: no profession gets more than two skills in any one primary attribute, with exceptions made only for the Folklore, Toughness, Rumor, Simple Melee and Simple Ranged skills.
Combat is faster, offers more options and removes a lot of the oddities from prior editions of WFRP. It also divorces the idea of hit point and wound tracking, using a narrative element to trend how hurt a character is, how much stress they're suffering from and when they suffer critical injuries.
Characters possess specific personality attributes, which rest on an "alignment scale" between Order and Chaos. Actions that are deemed to follow their order attribute can grow, granting additional fate points. Actions that follow the chaos attribute can grow as well, granting afflictions, madness, mutation and insanities.
I am not familiar with what the term "fantasy heartbreaker" means. I am assuming you mean whether this is a true retroclone or not. It is, but it isn't. In many ways, the game stands on its own two legs, differentiating itself from WFRP but feels familiar both thematically and rule-wise. I would invite you to read the "What Is ZWEIHÄNDER?" on the website here to learn more: http://grimandperilous.com/?page_id=8
In essence, it divorces the Old World entirely from its ruleset but embraces the down in the gutter, gritty aspect thematically throughout the work. We call this "grim & perilous gaming", which resonates throughout the work.
Download the short introduction chapter to learn more about ZWEIHÄNDER Grim & Perilous RPG here: https://www.dropbox....uction.pdf?dl=0