ZA = Down.

Me and the guild, Shattered Twilight, have been doing ZA runs for about 3 weeks now, and as of last week, we've cleared the whole instance.
I'll give you my insight of the bosses, in the order which we do them.
Akil'Zon = Eagle boss, I'd say one of the easiest encounters, this boss requires very little coordination, and it's easy to overcome.
Nalorakk = Bear boss, For Ranged/melee dps, this is just tank'n'spank, however, the tanks have a tougher job. Easy enough, if your tanks are up to par.
Jan'alai = In my opinion, the toughest of the animal bosses, the dragonhawks are a HUGE pain if you don't have a pally tank, for the rest of it, it's pretty easy dodging the explosions. My guild had him HARD enrage at 2%, We stayed alive for 9 seconds, and got him down. The tank reported that Jan'alai hit him for 26,000. Wow lol...
Halazzi = Lynx boss. Very easy fight, just have to watch out for the sabre lash, and the corrupted lightning totems.
Hex Lord = A tough fight indeed, Adds are never a problem, just spirit bolts and Soul Siphon.
Zul'jin = Easier then hex lord, IMO. He goes into 4 animal phases, the Eagle being the toughest for me. (unable to cast spells)

Well, that's it on the progression.
Thanks for reading!