Enough detail to guide you, not so much it binds you.
The thing to keep in mind is that the Diamond Throne is a gazetteer-style campaign guide. It's 96 pages, not a 240 page hardcover. So it's more useful to think of it as a campaign framework than a detailed world-spanning travel atlas.
Now personally, I'm a DM who likes to wing it a lot. Which means I steal bits and pieces of adventures, characters, items, etc. from all over the place. The setting is detailed enough that I have a good idea how things work ("Let's see, every city has a Speaker who represents the non-giant races and a Steward who really runs the place. Ok, cool.") while being open and flexible enough that I can drop in whatever I want to adapt. ("We'll put the Banewarrens in Ka-Rone and the Temple of Elemental Evil needs to be close to the verrik lands. Done.")
So if you're looking for something that's open-ended and suitable for a lot of tweaking and adaptation, it's worth checking out. In fact, if you're going to DM a game of pure AU, I'd say it's mandatory reading. It does a great job of fleshing out lands and monsters and giving you a better grasp of the world style. There's a lot of interesting racial dynamics to AU that are a lot deeper than "We live in the mountains, you live in the trees. Now we fight!"
But if you like a super-detailed setting that includes chronological org charts of who's living and who's dead in Gyre Gymblecutty's Giant Toad Riders, then maybe DT isn't for you.
Personally, I pick up those books thinking that I will read them cover-to-cover and steal all kinds of great nuggets hidden in the various chapters when in fact I invariably wake up at 1:30am with the light on wondering why I was having dreams about being chased by gnomes on giant toads.
-Thrommel