They've got pictures up of four of the bosses, and info about the two last bosses, Hexlord Zin'jakk and Zul'jin himself, that we'll fight together. The first boss (whichever one that is-- I thought it was the Bear boss, but that fight seems more complicated) is supposed to be easier in terms of raid coordination, but Zul'Aman is definitely a continuation of what's going on in Karazhan, according to Blizzard. They say the difficulty will start around Nightbane or Prince and head upwards from there. Also, as we've heard, Zul'Aman will have a timed quest similar to the Baron Run, where you can try doing the instance quickly to earn better loot.
Exciting stuff. I usually stay away from the PTRs, just because I like seeing stuff when it's released live on the realms, and any progress I make in the PTRs is eventually lost. But 10 mans are always fun, and I love the Zul instances, so whenever the PTR hits this week, you just might find me there taking down Trolls.