My fascination with the real John Dee led me to this book and I thought, "Hey, I enjoy YA fantasy," and picked it up at the library. It didn't start strong for me, but by the end I enjoyed it well enough to consider checking out the second book at some point. 
 It feels much like the set-up of the Harry Potter or Percy Jackson books, with the modern young protagonists (twins, in this case) stumbling upon their grand destiny thanks to run-ins with magical adults. In this case, the adults are based on real people: Nicolas Flamel, his wife Perenelle, and John Dee. I won't say who else shows up, but there is an interesting mix of historical and mythological figures. It's not the deepest of plots (so far, anyway -- the other books could change that), but I generally don't mind that in YA if it's a fun story, and this was. 
 My issues with the book were fairly superficial, but they added up. For example, the frequent mentions of modern technology (laptops, iPods, cell phones, etc) felt forced and in some cases missed the mark. In one scene, one of the twins was looking something up on the web and used Altavista as his search engine. Sorry, but even in 2007 when this was published, a web savvy teenager would have been using Google. The character did ultimately use Google and find what he was looking for, but... eh. It was stuff like that that pulled me out of the story and caused me to make scoffing noises. I could imagine a lot of those details making the teenagers relatable to young readers ("He has 60GB of mp3's? So do I!"), but these elements will also date the work (and annoy certain adults, apparently).