Open Grave - a quick look
For DMs, the book is moderately useful, more so if your campaign focuses on an area with a lot of undead *cough*Morimar*cough*. In addition to an assortment of monsters and options for more modifying monsters (great for when your players have memorized the Monster Manual), there is a spread of encounters running the gambit from low level to epic. I glanced at a couple of low level artifacts that I wouldn't actually tremble at letting my players get their paws on.
As I said, there was a surprising lack of material useful for non-DMs. There were a couple of rituals and that seemed to be about it. I figured there would at least be some paragon paths and magic items around the undead/fighting undead theme.
For DMs, I'd give this 3 necromantic undead flying monkeys. It's only worthwhile if you want to use a lot of undead. For players, don't bother.