Warning #1: these reviews are totally idiosyncratic. They're all about whether my daughter would like the book, so YMMV.
Warning #2: I include spoilers galore. I'm assuming that you don't want to read these books yourself, you're just looking for books your kids will like.
Warning #3: My daughter loves Harry Potter, so my reading tended toward fantasy novels. I won't be reviewing any Babysitter Club books here. (Wait, is the Babysitter Club still a thing?)
Warning #4: I'm a nasty, snarky reviewer. My nasty, snarky comments about the books I'm reading drive my husband nuts. You've been warned.
Alright, first review:
The Inheritance Cycle, by Christopher Paolini (includes four books: Eragon, Eldest, Brisingr, and Inheritance)
Stop me if this sounds familiar: A beautiful princess (Arya), on a dangerous mission, is waylaid by the dark minion of the evil Emperor. In her desperation, she sends the precious treasure she is guarding to the only person she thinks can help, a once-powerful warrior – one of the last survivors of a noble order of magical soldiers – who is now living peacefully in the back of beyond under an assumed name. Instead of going straight to the old man, the droid...er, dragon, is picked up by our hero (Eragon), a young man of uncertain parentage, living with his uncle on a remote farm. Because of the dragon, the boy is not at home when the minions of the evil Empire track the lost treasure as far as the farm, and our hero returns to find his home destroyed and his uncle dead. He sets out to get revenge, meeting a long-lost sibling (whom he hadn't known he had lost), while being tantalized by visions of the beautiful princess, who has been imprisoned and needs his help to escape. He succeeds, but only after his mentor dies to protect him while battling the minions of the evil Empire. Our hero then travels to a dense, green forest where he meets a pointy-eared ancient warrior of the old order, the one-time teacher of the mentor-figure, who teaches him the way of the Force...er, magic. But, he hears his friends are in trouble, so he leaves his training, despite the teacher's warnings that he's not ready. Unprepared, he is confronted with dark secrets about his parentage, and....
OK, you get the idea. I found the highly derivative plot quite distracting. There was literally a scene where I expected the mentor-character to say “These are not the droids you're looking for.” We are saved from the “Luke, I am your father” scene only by luck. Other derivative features include Edding's silvery hand marking and McCaffrey's sentient, telepathic dragons. Give the author credit, though, for improving dramatically upon the Tokenien orcs.
The writing is also awkward, although it improves over the course of the series. In the first book, some of the descriptions literally made me wince, like this one from page 15: “A bit past noon he heard the Igualda Falls blanketing everything with the dull sound of a thousand splashes.”
On the other hand, the books were written by a sixteen-year old, and they represent a significant achievement for a teenage author. Most sixteen-year old's wouldn't have the discipline to write a full book, much less four books of this excruciating length. So, good on him. The characters are interesting. He does a good job of world-building. I can see why young adults/children, in particular, would be pulled into these books.
Age-appropriate for a 7 year old?: Yes, except for the length. Each book goes three hundred pages past boring, but there's no inappropriate language, graphic violence or sexual content.
Positive gender roles?: There's only one major female character, Arya (the princess). She's a standard powerful-bad-guy-killing-but-still-pretty-and-primarily-a-love-interest kind of character. On the other hand, Arya and Eragon (the main character) don't actually end up together (although it's implied they will eventually). The portrayal of masculinity is pretty standard as well (focus on being a warrior, leadership, honor). For gender roles, I'd give this series a "meh", maybe a "meh plus", just because the love story doesn't have a standard ending.
Does the book reflect diversity in any way?: Not so much.
Final verdict: I won't read this as a bedtime story. If my daughter gets desperate for epic fantasy, I'll let her try this and see if she gets bored. There's no harm in the story, but it's too long for elementary school children, and there's nothing particularly good about it, either.