The guy has the potential to be an excellent manager. He has spent a long time researching and studying the methods of top European clubs, and knows how he wants the game to be played.
The biggest problem he has appears to be dealing with the Board. At his last two clubs he has fallen out with the Chairmen because he didn't get exactly what he wanted, exactly when he wanted it.
Similarly, when he was being touted for the Scotland job, he basically talked himself out of it before he was even interviewed, by mouthing off about what a poor job the SFA were doing, and what would need to be changed before he deemed it worthy of consideration.
If he can keep that side of his ego in check, he could do well at Forest. He certainly likes his teams to play a bit of football, which should suit your club.