Was a great book, I really liked it. It's not my favourite, PoA still holds that spot, but it wasn't my least favourite, either, it was good! I loved Dumbledore in this one... and learning everything about him. It really strengthened how much I like him as a character. I also loved Neville and McGonagall, and I was so sad about Lupin and Tonks, Fred, Dobby and Hedwig. ;_; I was pretty glad it turned out Snape was good.
My favourite line has to be: "Of course this is happening in your head Harry, but why on earth should that mean that it is not real?"