Read it and Weep
Animorphs Books 1 and 26
Despite its status as one of the seminal YA series of our generation, all three of us managed to miss Animorphs when we were young. Fortunately sponsor Anna was able to set us straight by forcing us to read book #1: The Invasion and book #26: The Attack. And now we're stuck as eagles for the rest of our lives.
It's a fun/dark science fiction series where kids can turn into animals because the world is ending. They fight a never ending war and sometimes people day. Like I said, it's dark. And sometimes they're tigers so that's the fun part.