The basic idea of COM is nice and simple, but then there are so many extensions and details that your mind starts to overflow. This book provides you with the basics, and then keeps on pouring the minutae in. It's a fairly solid technical book, but feels a little old. Coverage of the ATL (which I have yet to learn about) would have been useful. Put it this way: I borrowed this book from a friend, and may try buying a different book on the subject (partly for the contrast).
And no, I'm not a total MS sell-out. I'm just trying to get a little balance. :)