We tried real hard, but could only get Zul'jin down to 9%. That's not bad for a first try and I'm sure if we keep at it we will get him down. Zul'jin is an interesting fight and although you can read all about it on wowwiki (or even see videos), I would like to give some personal impressions.
First of all in terms of group setup, we found our more successful tries to be after we switched to a more melee/hunter heavy group with fewer DPS casters. Every caster means lost DPS in phase 3 as they can only wand, and the longer that stage lasts, the more in danger you are of a healer dying. In addition, probably because our DPS is a bit low, a 4-healer group was easier for this fight. A druid was practically a must for phase 2.
So much for group setup, now the actual fight.
Phase 1 is very easy as long as healers are quick about topping off people who get the Grievous Throw debuff. We had no trouble here. Tip for casters - save your mana, don't nuke, you'll need max mana for stage 2.
Phase 2 changeover is the first place where we (and I guess others) had trouble due to the agro wipe but also due to the fact the the boss almost immediately hits the tank hard very hard and then paralyses the whole group, including priests. Even with 2 Renews on him the tank (a warrior) sometimes went down (had 21k life buffed). Once we had a druid however we had no problem as the druid's HoTs were more than enough to keep the tank up until we were released. For the casters, this is the stage where you need to nuke all out (but watch threat) as you don't need to save mana, you'll get it all back during phase 3 when... You wand only lol :)
Phase 3 - hunters and melee can continue DPS and are advised to nuke as there is no agro and no damage from boss, only from the vortexes. I found this stage very annoying as both a mage and a priest, it was always a relief (on every attempt) to get past it. Tip - make sure every person has read the wowwiki guide and knows which abilities their class can safely use.
Phase 4 - we nearly always lost the person who was the focus of Claw Rage unless it was the tank or could FD/bubble/etc. The debuff was also nasty to heal let me tell you as you would have 3-4 people ticking for 1.5k every 2sec each. Almost every attempt that we got here, if we managed to get past it, it would be with fewer people.
Phase 5 - with the healers low on mana already from healing phases 3+4, and sometimes with dead people from phase 4, this phase was a killer. Partially people simply didn't move fast enough from the flame columns, sometimes it was because healers were simply OOM. Overall, if you compare this fight to Hakkar, or compare ZA to ZG, I would say ZA/Zul'jin are more interesting/fun than ZG. The only thing I dislike in ZA is the gauntlet. I think the boss fights in ZA are more challenging and require a greater amount of group coordination and individual ability than ZG.
Partially this is of course because ZG was build for 20man and not 10man. Furthermore I found the fight mechanics in the Zul'jin fight to be more interesting and challenging than Hakkar. For Hakkar, getting 20 people (in a non-hardcore raiding guild) to step into the poison cloud was literally mission impossible. I really don't remember any fight where at least one person did not make it into the cloud in time. So really the difficulty of the fight had more to do with coordinating 20 people and getting them all to understand what to do, more than the technical aspects of the fight. Furthermore, once you do a single cycle of dps Hakkar/cloud, the fight becomes rinse/repeat (with MC being the only really variable element). The fight becomes predictable and therefore slightly boring. With Zul'jin, each person has to change his tactics and the way he performs and this doesn't require all people doing the same thing, just people doing what they should for their class. The 5 different phases of the fight add spice and flavor to the standard 2-phase boss fight and really make the fight unique.
So even though we wiped (over 10 times I think) and didn't get the boss down, and even though we were not really well prepared, I still had a lot of fun. Heck, I got to see new content - that doesn't happen every day any more...