"Harry Potter and the Order of the Phoenix" by J. K. Rowling

It took me a couple of months to read this book.  Not because it is hard to read, or because it's 870 pages long, but because I knew what was coming at the end and I just kept dragging my feet about getting there.  Also, I was loving how much Sirius Black gets to be in this one!  He gets more page-time in it than in the previous two books combined, and I adore that.  So much Sirius.
(Spoilers in this paragraph if you haven't read this book or seen this movie.)  Of course, Sirius is also why I did...