In the Imperial faction of galactic politics: Not all that much he aint a diplomat (However, ive only read the books pertaining to Thrawn, and the Hand of Thrawn Duology)
Military side: I love him. From what I can tell after hrawn died, Pellaeon was second only to Thrawn himself in tactics, due to his studying, and learning how to plan campaigns.
He was loyal, dependable, and had a value of human life seen only in Thrawn in the Imperials. He promoted creativity like Thrawn as well.