Here's a couple of other reviews:
http://www.gamewyrd.com/review/473
http://www.rpg.net/reviews/archive/10/10609.phtml
I've got it, and like what I've read. Understand, it's pretty much a toolkit that you're getting.
You'll get options for how to handle different things, and then the "default" that the creator prefers.
It's focused on being low magic and gritty. It doesn't have to be run that way, but that's the default.
The rpgnet review says that the book tries to evoke a pulp feel. I'm not sure I'd really agree with that entirely. "Pulp" to me isn't as gritty as the default to GT seems to be.
You can certainly run games using the GT book. It's just that the style and presentation make it feel more like "toolkit" and less like "rule book". If that makes sense. Not a criticism, just something to be aware of.
Something that's pretty groovy is the Creature Creation section, as well as the GT gamemastering section. Those are both good enough that they got split out into their own mini product that you can get from rpgnow. Both include an Excel spreadsheet to make your life easier.
On the whole, if you're planning on sticking with a d20 based game, it's not a bad way to go. The fact that it's based on d20 Modern may or may not be a problem for you. Converting between d20 Modern and D&D d20 isn't as easy as you'd hope/think, so if you're looking to keep using a bunch of D&D books, you'll have some additional work ahead of you.
Also, most of d20 Modern stuff is focused on... well, modern settings.
I don't know if any of that's a help to you or not.