Genna: I know several people who cried at the end; even more of my acquaintances threw the book at the wall and left it there.
Kitty: The main character is Max, the leader of a small group of genetically modified kids. They're all young; at the beginning of the series, Max, Fang, and Iggy are fourteen, Nudge is eleven, the Gasman is eight, and Angel, the baby, is six. They're 98% human, 2% bird. They have wings. They can fly. And they're constantly being hunted down for it.
They grew up in a scientific facility called the School, where a ton of genetic experiments were performed on humans. The flock was the most viable, and thus the most valuable. But they had cruel, inhumane experiments performed on them (the best example is when the "whitecoats" as the flock calls them tried to surgically enhance Iggy's night vision and he ended up permanently blind). So, when Max was ten, a whitecoat named Jeb rescued them, stole away with all six bird kids to Colorado, lived there with them for about a year, and then...vanished.
They aren't the only genetic recombinants, just the most viable. There are other ones, more vicious and more expendable called Erasers. Their sole purpose is to hunt down the flock and drag them back to the School, dead or alive.
The flock manages to live by themselves for three years, functioning perfectly fine, until one day, Erasers come out of freaking nowhere and kidnap Angel, the baby, and take her to the School (in California).
That's where the series starts. The rest is a whirlwind of fights to the death, flying, freaking out, teenage angst, backstabbing, danger, drama, drama, drama.
It's very good as far as fandoms go. Quality-wise...well, it's not the best-written series in the whole entire world, and there are certainly improvements that could be had. But it's still my favorite series, an extraordinarily enjoyable read, and highly recommended by yours truly. :]