This was the best book I've read since Name of the Wind -- and NotW was the best book I'd read in years. Black Prism is fully NotW's equal, though they're very different books. Face paced yet subtle, and you're constantly recalculating what you thought you knew about various characters. No character is simplistic, no one is clearly the good guy or the bad guy, and yet you still love Gavin Guile (the Black Prism) and Kip (his... nephew, aka bastard -- the ...nephew bit is a running joke throughout). Nothing is predictable and there's not a single page that's boring. 
 The magic system is interesting and unique and revealed slowly, in a way that doesn't drag the story down, but what makes this book really kill is the characters. It's one thing to tell you that a main character is powerful and handsome and has an amazing body and he's charismatic and everyone loves him. Most authors do this. (See: every vampire book ever.) It's another thing to *show* how charismatic Gavin Guile is and why everyone loves him. It's yet another thing to write a secondary character who is fat and clumsy and bullied and rather pathetic (Kip), and yet still make the reader love him and root for him. It helps that Kip is wickedly funny and I was laughing out loud nearly every second page over something he either thought or said or did. 
 A measure of how much I liked it: I'd bought an ebook version on sale for $3, having never heard of it before. Halfway through reading it, I went and ordered hardcover copies of this book and its sequel, because I knew I would want to have this on the shelf forever, and read it again and again. 
 No, here's a better measure of how much I liked it: I often finish books knowing that I'll want to re-read them -- eventually. This is the first time I've finished reading a book and immediately started re-reading it. 
 I hear the author's wife supported him for years so he could write and not work. If I knew the woman's name and address, I'd send her flowers and a thanks. I can see why she did it, too -- I don't even know the guy and I want to support him so he can write the third book and never have to work.