I've flipped through it in my FLGS, and I really must say that while I was pretty excited about this (and the fact that I could buy it, since I got hired for a nice job and will have some money to spare, for once), I'm pretty sure I'm not going to buy it.
Overall I just found the book relatively blah, especially compared to MotP, which I think it one of the best books WotC has put out. There are a few good ideas in there that I'd probably never use in a planar campaign, as opposed to stuff from MotP. The Planescape stuff is nice, but not nearly enough to make up for the whole book. If I could find it somewhere half off I might pick it up, but otherwise it's a pass from me.