My opinions about this book are very similar to yours; it was the first time I couldn's say aloud "this book is the best of the series", wich I used to say of every book after finishing them!
The main feeling is that this was meant to be a 'postOtTp' and 'pre-7th book' book, with no real "personality" on its own. A lot of things happened of course, but more things remained held over. I hope the last book will make up for this!