It also has a sequel series, so there's six decently long books to read. Definitely one of the coolest magic systems out there. To expand a bit on how it works: gunpowder is basically a drug, as mentioned, but powder mages can also burn gunpowder near them and redirect the force thereby generated as they like, so they can make a bunch of powder explode next to them and direct the blast away from themselves, for example, and one character can fire a bullet and make it shoot much farther than it could ordinarily go by expending powder on his person and using the force from it to push on the bullet.