Indispensable.
I absolutely hate the way technical interviews are done for programmers. Can you imagine if a heart surgeon went to interview at a hospital, and they handed him a game of "Operation" to play? That's how we interview programmers. It's so stupid, I could go on and on about it for paragraphs.
But, if you want to work at the top tech companies in the world, you have to play the game, incredibly stupid and poorly aligned it is to the task at hand. And if you're about to head out on some coding interviews, reading Cracking the Coding Interview is the single most important thing you can do for yourself. It's simply phenomenal.
There are definitely some sections that Gayle doesn't seem particularly interested in. For example, the coverage of Bit Manipulation seemed a bit cursory, like it's an area that she's not super familiar with or comfortable with herself. But for the most part, all of the major stuff is covered, in the right level of detail. It's good to review but if you weren't already somewhat familiar with a lot of these data structures and concepts, I'm not sure that the book works as an introduction.
One major omission is the coverage of Tries. They get a shout-out as a data structure that basically doesn't show up in interviews, but I interviewed at 5 major tech companies after reading this book and Tries were the right solution in three of them.
Overall though, the reason to get this book is for the set of questions. Questions that are exactly the kind of things you get asked in coding interviews. Each question has some hints, as well as the answers in the back. Take the book, and practice solving the problems on an actual whiteboard. Don't skip to the answers, but feel free to read the hints (most interviewers will provide similar hints).
There's simply nothing else you can do that better emulates the coding interview than practicing the problems in this book. It's a must-have.