You guys made it all the way to Book 6?
Book 4 was the last one I read and the last one that appealed to me.
For years, I never understood why I couldn't get into the fifth book and I've only now just realized why.
I loved the individual adventure in each Harry Potter book but I didn't really care about the overarching plot. When Voldemort came back and it started building up to Harry fighting him in Book 7, the series lost its appeal for me. It wasn't a series of adventures anymore, it was about a prophecy and destined battle. It became way too focused, way too predictable, and way too generic.
People wouldn't shut up about trying to guess who died in each new book. The fact that someone had to die at the end of every book after Book 4 seemed stupid to me, even when I was 14, waiting for the fifth book to come out.
I didn't get too far in Book 5, but from what I've read from it and the movie, it's essentially Harry Potter and the Shitty Angst Year.
Really, I wouldn't have minded if Voldemort stayed dead and the series focused on Harry and his friends getting involved in more mysteries based on the things that Voldemort left behind (his diary, his followers, etc).
I doubt anyone in the world agrees with me though.