What separates a decent hack and slash from a truly memorable one, for me, is when the action serves the world and the protagonist's growth, not just their kill count. I've slogged through so many where it's just a montage of cool moves against interchangeable baddies; you forget who died by the next chapter. But take something like 'The Rage of Dragons' by Evan Winter. Sure, it's a relentless, brutal training and revenge arc, but every fight—whether a duel or a large-scale battle—feels like it chips away at Tau's humanity, forcing him to become the monster he needs to be to win. The 'hack' is physical, but the 'slash' is psychological. You're left feeling the exhaustion and the moral cost, not just pumped up.
Plot-wise, a great one needs stakes beyond survival. If the goal is just to clear a dungeon, who cares? There has to be a tangible, emotional objective woven into the violence. Rescuing a sister, preventing a ritual, proving a point to a corrupt society. The action becomes a means of expression for the character's rage, grief, or defiance. The best ones make you feel the impact of every parry and thrust on the wider story, like a single combat deciding the fate of a rebellion. It's not mindless.