I seem to differ from other reviewers in that I found the first part of this book to be the most interesting. The authors display the City and its culture for us, rebellious hero Kellen learns about Wild Magic, etc. After a while, the discovery slows, and the story becomes formulaic. Sadly, that only continues as the book progresses.
I found The Outstretched Shadow to be a readable YA fantasy, but it didn't go beyond that. The characters were pleasant, but not intriguing - they pretty much all fell into familiar categories. The story was more problematic, suffering from two key weaknesses. First, it was not original. That need not be a fatal flaw, but it's not helpful. Everything we see in this book, we've pretty much seen before, and the authors didn't even seem to try very hard to do anything new. Second, and more important, the story and plotting are a little too free and easy. Everything happens as it must to suit the plot, and there are virtually no impediments to progress. The descriptions are good (if they run long), but the events are entirely unsurprising. You know where this book is going halfway through, and then it's just a long, mildly diverting plod to get there.
Finally, the ending - climactic as it is - makes virtually no sense.
Overall, harmless YA epic fantasy, but it's hard to suspend your disbelief long enough to really enjoy it. I can't recommend this when there are many better stories out there.