I expected to like this book, as I think Cornelia Funke is an excellent writer. I think I was also expecting something of the caliber of 'Inkheart', which this frankly isn't. In fact, I did something with 'Reckless' that I almost never do: gave up half way through. I just couldn't engage witht he story on any level, which is a shame because the presmise and themes are interesting (alternate world accessed through a mirror, troubled sibling relationships, ticking bomb in the form of a curse)but somehow they never become any more than that. The characters and their struggles were wispy, half-drawn, just too thin to care about. Likewise the 'love story', which left me completely cold, (and which, incidentally, plays a far smaller role in the story than the blurb and taglines suggest.)
I think part of the problem is that the characters are actually adults, not girls and boys as the back cover suggests. This makes them hard for the intended audience to relate to, but the problem is bigger than that. Because they are adults, the story picks up long after the main character has discovered the world beyond the mirror. This is a huge mistake, as a major element of successful books in this genre is escapism and wish-fulfillment for the reader. Here, though, the reader loses out on the excitement and adventure of discovering the new world with the main character. Likewise the romance, and even the mystery about the brothers' missing father: we hear about all of it, but don't experience any of it, so it's hard to care. Classic case of show, don't tell.
I think the other issue is that the publishers are clearly trying to market this book as a teen supernatural romance, which, quite bluntly, it isn't. And that's unfortunate - it might generate a few sales, but I very much doubt that young readers will be coming back for more. That's a shame, as they'll miss out on Funke's other, better books.