I never really cared for the breed until I read about them. The International Encyclopedia of Horse Breeds
by Bonnie Hendricks has some great information, and it really gave me a respect for the breed and its history. It's amazing to think that they may be even older than Arabians, and are thought to have been the main contributors to the Arabian breed (Arabian lovers would probably come after me with a pitchfork-wielding lynch mob if they heard me say that).
Anyway, I've never worked with one, but I hear they're a lot like Thoroughbreds and Arabs - hotblooded, but sensitive and intelligent. They were warhorses back in the day, so I imagine they must be of fine temperament. At least the high-quality ones.