I applaud the makers of this show. Expertly crafted, based on a brilliant book, and best of all it doesn't go out of its way to be a "children's show". The characters are complex and given what they're routinely put through every episode, you really feel for them throughout the series. Even an adult like me found Silverwing to be extremely enjoyable. The animation is great, the music is spectacular (especially for a cartoon), and the chase sequences (of which there are plenty) are truly thrilling. It does have quite a few dark moments, but they don't dominate the show; they actually make the high points that much more rewarding, and that's something I feel is sorely lacking in a lot of cartoons out there. It reminds me a lot of Sonic The Hedgehog - The Complete Series in that regard.
It follows its source material pretty well; much of what's found in the book is seen in the series, but the series takes it further by adding more to the story. Here we see what goes on among other characters besides Shade and Marina; we see how the rest of the Silverwing colony braves the long journey to Hibernaculum, as well as how Goth and Throbb have been affecting the rest of the animal kingdom, and there are some good side-stories woven in there.
I do think it's a shame the series didn't return for a second season, but there's some good closure to the show and I'm glad it got to make its run on TV.