That was a cool, fun trip! I have fond memories of my mom reading to me and my siblings when I was a kid, and I've enjoyed passing the tradition along!
And now -- since this story has been taking up so much of my brain of late -- I have to give you my promised critique:
1. The evil-just-for-the-love-of-evil villain. My kids already spend enough time on commercial stories that are designed just to sell toys (eg. Lego Hero Factory, Planet Heroes) where they make a simplistic division into bad guys and good because its the easiest way to give your hero a conflict. And I know that Voldermort had some depth and character development (he sure a hell better have some, in 4176 pages...), but I think that an excellent children's series ought to have a more imaginative quest/conflict than the usual "We have to stop Dr. Evil from destroying the world because he's so evil just because he loves evil."
I found Lord Voldemort to be an incredibly boring villain. The series makes up for it a bit by having a number of interesting side characters, like Snape. I liked most of the teacher-characters, though (as my husband pointed out) it's a bit odd that none of the teachers are married or have a significant other. Did Rowling forget to mention that accepting a teaching position at Hogwarts means you have to take a vow of celibacy?
2. The monotonically increasing level of evil. To borrow some Dungeons & Dragons terminology, Rowling's series feels like "Lawful Evil" compared to, say, some works by Roald Dahl which feel more "Chaotic Evil". In Potter-land you don't get the feeling that anything might happen (unlike, say, Alice in Wonderland). It's more like Science Fiction than like magic -- the characters have a specific set of additional powers/technologies and a particular set of alien creatures, and they're all plodding towards the epic battle. And if there's X amount of violence and death in book 1, then the amount in book 2 is X+1, etc., so that by book 4, it's already pretty questionable whether it's appropriate for children, and by the last book, so many people were dying noble, glorious deaths in battle that I felt like I was reading a Klingon opera.
3. Underdog! After the beginning of book 1, Harry's not really an underdog anymore, and yet a lot of the story seems to rely on the reader rooting for poor Harry. Some of the situtions the author constructs to repeatedly try to put him back to underdog status (he's stuck at the Dursleys' again, Snape is mean to him, Dumbledore won't tell him everything) seem contrived and petty. I feel like I'm not explaining my point very well, so just consult this Potter Puppet Pals episode:
For such a long series, it might have been more interesting if the POV didn't always follow Harry. As I said earlier, I felt the "Dark Materials" trilogy did better than the Potter series at having peripheral characters take important independent actions rather than having all the action revolve around one or two battling champions. (And those battle scenes! Everyone picks a partner and starts duelling, as though it were the Yule Ball.)
I have a couple of other picky complaints, but I'll just leave it at this. Despite the occasional annoyance, I really did enjoy reading these to my kids. But now that it's done, they're asking me to go back and read them selected chapters! I'm happy to keep reading to them, but I'd like to move on to something new. Suggestions...?