From the introduction:
Many Roleplaying games that involve magic try to limit it, or balance it in some way, to allow all the other types of hero to fight alongside them on equal terms. Grimoire, however, is not that kind of game: instead of sharing the limelight with mundane heroes, every Player Character is a Wizard with access to a nearly unlimited supply of magical power. If you’re a Game Master looking to stick your players firmly beneath the pointy hats of a group of wand-waving maniacs, or if you’re a Player looking to be a wand-waving maniac, then Grimoire is the game for you!
Adventures in Grimoire are sometimes serious, but more often wacky and hysterical, and told in the Narrative style. These adventures are normally challenging to Wizards, who know little other than the magical arts, while the situations can rapidly escalate from the banal to the incredibly lethal as the result of their own bungling incompetence. Not that any Wizard would admit the situation has gone anything less than according to plan.
Grimoire also differs from most roleplaying games in that Player skill and involvement is as much a part of the fun and chaos as anything else: a Wizard cannot be more competent than their player.