I didn't read 'em for a while - usually what is popular with the masses is dross to me. My librarian friend said they were good stories... and they are.
I would definitely start with the first one... and it's a bit of a slow start, too. Hang on... once you're in, it picks up and is tons of fun.
THe fourth book or so things do change radically and go from kids' adventures to darker stories that involve the whole world.
I do sympathize with an English prof here who said she stopped at the third book because she was disappointed that the whole society had such strictly stereotyped roles, especially gender roles (but not limited to that). I'd already accepted that... that this was a story of heroic action by very imperfect people in a very imperfect society (and I love how the wizard world's "little issues" unfold... goblin politics and all...) tho' there are chapters where the teenagers are being so annoyingly Teenager that it's almost like watching a soap opera and I wish they would just GET OVER IT
Most folks I know figured that she'd find *some* way to give us a Snape Surprise. It was a little bit "out there," since Dumbledore's behavior wasn't quite typical of him... you'da thunk he'd learned... but all in all, very satisfactory.
Here, I could pay in advance and get in the "pre-paid" line with my ticket at midnight and trade ticket for book... *very* fast-moving line. Then ride home, read 'til 2:00 a.m., go to bed and get up and lead my bicycle ride, pause for reading occasionally (when we stopped to eat), back home for a nap, read, eat, finish it... gotta tell you, my dreams were sort of invaded and I had to sort out book from dreams at one point!
For kids? Welp, it gets pretty dark.
I read a post from a teacher and mom who had trouble 'cause of the "B" word, whereas I realized I had trouble with the situation wherein it was used; it portrayed vengeance-is-the-perfect-climax. (The idea that that was no problem, but saying B**** was rather disturbed me. It's okay to kill, but be polite while you do it ?!?!?)