You can read the Goodreads summary here.
I thought I was really going to love this book because the description sounded great, although cryptic. Charlie lives in a world where there are actually two worlds on Earth, that with seven billion humans on the Earth's surface, and that with an unknown number down in the Earth's core. Charlie also has weird dreams he can't explain until he travels to that other world and learns who he really is.
Totally thought this book was going to be about a secret alien invasion. I was wrong.
Ultimately, I had two problems while reading this book. First, I felt like the plot was too linear and at times characters were doing one thing after another without much description as to why they were doing it. Second, sometimes things seemed a little too convenient. On a more technical note, the book takes place in England and the characters often refer to drawers (as in, open the drawer and fetch me that thing) as draws. This came up several times in the book, even in a chapter title. I don't know if this was an error if they really call them draws in England.*
Unfortunately, this was a two star book for me. It didn't hold my interest at all and by the end I was skimming. Talisman of El really is of the fantasy genre though, so that's part of why I didn't care for it. Fans of Artemis Fowl would probably enjoy this book. If you're interested it will be release May 20th.
*Note: I tried to Google it and couldn't find an answer, though I did find this oldie but goodie posting from Craigslist about it.