If you're a fan of Grimdark, you MUST have this book and its sequels in your library. It's reminiscent of Abercrombie, Erikson or Cook, but has a lot more humor. These are hefty books, but you'll zip through them because of how fun they are.
This first book introduces us to the Reaper, a nasty warrior without equal (and the series' protagonist) who is called upon to destroy a dangerous and insane wizard. The supporting cast of characters is sublime, too!