Internet problems prevented me from telling you about the Tribes of the East videos that were taken at Chinajoy 2007. During a short tutorial mission you get to see creatures, Stronghold heroes and the very peculiar orcish spellbook. The quality of the movie is mediocre and you can't hear much, but seeing the content of the expansion in action is quite exciting. DaystarDragon was kind enough to put them on Youtube:

part 1 | part 2 | part 3

In the forums, Eternor posted a couple of pretty screenshots showing the Orc faction in action. In this thread, evilp explains briefly how combination artifacts will work.