I've read the first two and want to start the third. I've enjoyed them so far, and they weren't really that scary (like I feared they would be). But you just can't get around the fact that there are 24 kids put in an arena and only one is to come out alive. That just sends chills up my spine.
I asked a middle school English teacher about the books, because I was still just so shocked that the audience is tweens and teens. She said she has had her 7th and 8th graders read it and discuss, but she felt the 6th graders are too young.
My 12 year old niece is reading the first book, and I was talking to her dad about it (he wasn't so sure this was a good book for her to read). One thing we agreed on was that reading a book and imagining it are very different from seeing it on screen. Some kids just can't comprehend it, so they just kind of skip that part in their minds. If it's on screen, they know.
I haven't seen the movie (and my kids are very young), but I really don't think I would let anyone younger than high school see it.