I wouldn't describe it as the worst but I'd say it is not gripping. Half Blood Prince and the Deathly Hallows are gripping. Remember, the 5th book was also a very dense book because JK Rowling wanted to fill in a lot of information that hadn't been given in the preceding books.

So, in terms of how it keeps you excited, it failed but the book packs a lot of other useful information which were referenced in the books that follow.