I've only known two Hanovarians. The first is an older gelding. His gaits are amazing, although he's really stiff and arthritic(sp?) now. His tempermant is pretty good and apparently he used to a quite an eventer is his hay day.
The other Hano I knew was a younger mare and she was wonderful under saddle and over fences. However, she had horrible ground manners, was extremely hot, and generally hard to get along with. In fact, she was hotter than the TBs I knew.
Like others have said, it depends on the particular horse, not the breed.