I give this book 4.5 stars, and mind that I'm in love with the Mistborn series,* which is part of what made me love this book.
It's books like The Alloy of Law that let me know I actually CAN read quickly, should I put effort into it. This is the kind of book that makes you put off work to find out what happens. Mistborn has the most fantastic magic system of any fantasy I've ever read, and it's that system that really drives the books toward excellence.
The story itself is rather good, a mystery with fantastical elements and a western twist. I liked the protagonist for 99% of the story. The way he deals with the complications in his life seemed very realistic to me, even at the end, when he made the choice I didn't want him to make, despite knowing that, for his character, that was the best choice for him. It's definitely interesting to see how Sanderson handles the "romantic" plot line in this novel.
My only gripe with the book is the occasional forced humor, whether it's in funny jokes that go a little too far, or an attempted laugh inserted in an inappropriate place. A lot of the humor depends on the reader, however--while I had a few [minor] issues with the comic relief character, my husband loved him, so all is well.
One of the best parts of the book is the references back to the original series. (I'd like to note that, without the support of the original trilogy, this book would have been weaker. Then again, I doubt anyone would read it without having read books 1-3.)
Be warned, Brandon likes to leave a few loose plot holes to drive you mad. ;)
Side note: I thought, based on the cover, that Waxillium had a really long braid, but that is just the fringe of his coat. My little fangirl heart broke a little.
*The Mistborn series is, by far, my favorite books of all time. I've never reread them, since when I plot my own novels I always find myself trying to steal from it (at which point I slap my hand and start over, I have a thing with originality), but after reading TAoL, I think I shall revisit my old friends... (I have a HUGE crush on the eunuch, after all...)