A great product for all arcane classes. 5 highly flavored cultures, which can integrate all arcane classes from the PHB 1 and 2. The fluff is really good, the book is very well organized and it is easy to read, even on screen.
My only concerns are on the mechanics side. I didn't see any major balance issue, yet I feel there is something missing. I expected more powers, and a few paragon path as well. On the alternative class features, some of them were quite interesting, but others are less attracting (not from a lack of balance, though).
[4 of 5 Stars!]