I played the adventure in the back of the book and the prophecies of the dragon campaign.
Overall, the game was a rousing success, but thats because players actually went out to read the books after the first few games and really got into their characters, character histories, and so on. It really makes more sense if this is the case. I would suggest that this be a character motivated game rather than a get the doohickey one.
Also make room for large periods of time when characters are, for instance, training or travelling.
OK - Classes are good, if somewhat front loaded. I quite like the Woodsman, and even prefer him to the ranger, for instance.
Channelling. This is not overpowered in my experience, but can be quite robust. Half the time by the time the channeller touched the source the combat was half over, so that wasn't the issue. The bonus feats the male channelers get also are not so much of an issue because of this fact; before the channelers really get going its all over. The madness wasn't so much of an issue in my game (My sole male channeler had his character not actually knowing he was affecting events, for instance.)
The way our game was successful was more because the players weren't trying to munchkin things, but rather by playing, for instance, an Ogier in a town full of people accusing him of being a trolloc and a group of fellow PC's that are trying to convince the town otherwise.
Also - just be careful to really creep out the PC's with the wrongness of the shadow. Don't be afraid to really hit them with the muscle or creep them with the creepy; don't just have fades or Drakhar as things to come across in a dungeon. I made a party of 8th level PC's shiver inside a half-ruined tower as a Dragkar was singing outside, for instance.
Just try to hit the books feel and it'll work itself out.