This is one of the seminal Batman stories. It's where we learn about what happened to turn Joker into the madman he is, and where Barbara Gordon's career as Batgirl ends. It's a dark, dark story that makes you turn every page, curious what will be revealed next.
The copy I got was the deluxe edition, which was recolored by the original artist. The colors were part of what made this so brilliant. It was so muted, except for splashes of color to make a point. It FELT like you were reading something old rather than something new. And of course, the story was written by the incomparable Alan Moore, so there are a lot of twists and turns that you aren't expecting.
I don't recommend this book for the faint of heart. As I said, it's very dark. But it's also a very telling story, giving the reader a new look at the Joker. Even while I was horrified by the things he did, I felt sorry for the things that happened to break his mind the way it did. If you can handle the darkness and want to know more about the Joker, then please pick it up. I don't think you'll be disappointed.