I almost forgot to write something about Harry Potter six, but here it is, and spoiler free too.
As far as the plot of the book goes it is probably the most simplistic and straightforward of all the books plots. That is understandable when you realise that this book has been clearly designed to link the story to the final book by setting up the universe for a big fight and filling in some holes left by the last book (like with the Joke shop and Harry's inheritance). The biggest significance in reading the book is that the backstory to Voldemort is filled nicely. After reading the book he feels more like a proper character in the universe as opposed to a mythical entity that occasionally appears or is backreferanced.
It is a good book and my only grudge is with the ending, specifically with the identity of the Half-Blood Prince because the identity is revealed in a fairly flippant and inconsequential way. Usually with revaluations in the series, the revaluation will make you realise and understand more about that has been going on and from then on change the universe in some way, but the revaluation of who the half-Blood Prince is doesn't have any real consequence to this book or any of the previous. I am sure it will be very relevant in the seventh book, but it left me with an underwhelmed feeling.
Unusually for a Harry Potter book the story is left with a clear open mystery to a note that is found. And also the book has some cringeworthy moments that will make everybody consider wither the series should still be considered a children's book.