Singularity is a science fiction book written for older kids, bordering on YA. It was originally published in 1985. It may be a little obscure and old, may seem like just kids sci-fi... but it's every reason I've ever read a book. It was ABOUT something, but something so hard to describe... the only thing I could say when I finished the book (in one sitting of four or five hours, as I recall) was "Oh, my God."
Barry is like every fantasy/sci-fi villain, only back when they were sixteen. He's cruel, self-centered, reckless, power-hungry, and he can charm or coerce anyone into doing whatever he wants. He's frightening. Harry, his twin, takes a little longer to understand, and by the time you do understand him you realize you might not have understood Barry as well as you thought.
The book is tightly written, only necessary things are included. A lot of the plot is internal and it may seem slow, but it is crucial to understanding the point. By the end, you have that painful and yet exultant feeling of understanding everything in the world, simply because you can't put any of it into words. Singularity gives me the feeling sci-fi always did when I was a kid... the feeling that the universe is so much bigger and so much more magnificent than I could ever hope for. The feeling that there is still something to strive for, and that there are things so beautiful they make you feel like crying.
I hope someone else will pick this book up and discover that same feeling while they read it. (But then, isn't that the point of every book we recommend? The hope that someone else will be touched in the same way?)
I've loved every book of William Sleator's that I've read, most acutely this one and Interstellar Pig, and I will continue to search more of them out.