Karazhan was the first major instance in WoW:TBC, offering a relatively easy introduction to the world of raiding in manner allowing people to gather a small group of friends, or rather two five man instance groups to get together and raid. The traditional party setup of:
2 DPS / CC
1 "5th Man" class
Worked well, most starting Karazhan groups needing 2 tanks, and indeed some bosses virtually demanding them, 2 solid healers with one of the "5th man" classes filling in either as a backup healer or as a fully fledged healer. Overall the instance fitted into the progression structure nicely, at least from one side, groups banded together to form Karazhan groups and progressed through it, no fight in it really requiring any specific setup bar perhaps the early Nightbane which nearly insisted on a warrior main tank. The issue arose when moving from Karazhan to 25 man raiding, no longer could your groups simply combine, 2x Karazhan groups isn't 25 people, and those 25 man raids don't cope well with the 25 man raids, perhaps the best suited is Magtheridon allowing the use of 5 tanks during the initial phase, and 3 tanks for the trash pulls, Gruul in contrast required, or at least preferred 3 tanks with the third often sitting idle. The healer ratio really ate into the "5th man" slots as well, no longer a single healer per tank and the potential for off-healers but now requiring raid healing and massive main tank damage.
Most guilds make this transition however, or have their aspirations crushed and forced to remain in Karazhan or PuG these instances, I am not sure if this was really a design goal of Blizzard, and indeed the arrival of 10 man instances in WoTLK suggests otherwise, that raiding acting as a dividing force was a mistake. Zul'aman is thus an interesting prospect, its a 10 man instance introduced late in TBC, offering a "progression" path from Karazhan and the ability to be run by most guilds upto BT for a variety of rewards. The introduction of timers, arguably a good choice to maintain interest in this zone from higher level guilds, is however apparently very divisive.
The first thing to look at is the fact thats its a 10 man instance, once again we have the issue that Karazhan presented, but instead in reverse, we are attempting to take a 25 man raid with few tanks, many healers and cram them into this new structure, and the timers alter this. A normal non-timer Zul'aman run normally looks something akin to:
MT - 18K health fully buffed to ensure survival on Lynx
OT - 15K+ health fully buffed, takes the split damage and off-phase bosses
Healer 1 - Main tank healer
Healer 2 - Main tank / offtank healer
Healer 3 - Raid healer / support
DPS 1 - Typically a hunter for tranquilising shot
DPS 2 - Typically an AoE class
DPS 3 - Typically an AoE class
DPS 4 - Open slot
DPS 5 - Open slot
So accounting for a typical structure ZA fits well into the:
5man -> Early Karazhan -> Heroic 5 man -> Late Karazhan -> Early Zul'aman -> late Zul'aman
progression, that is it supports 2 tanks, 2 healers, a variety of dps and forces one of the "5th man" slots to be a healer, but retains 2 slots that are basically open to any class regardless of capabilities. The above structure is what is typically run that I see, thats not to say it can't be done with 5 rogues in the dps slots (and I have run timer runs like that :P), but its slightly harder to do so and doesn't give the best chance vs each boss.
The timer runs however change this, typicall a 2 timer run can be achieved using the setup above at the correct gear level, 3 timers easily achieved with a tier 5 gear level group, though often too short on raw dps for the 4th timer. To achieve that most groups alter their structure to something resembling the following:
MT - Preference to a paladin tank for gauntlets, and Dragonhawk
OT - Preference to a Druid, or a semi-fury/arms build warrior
Healer 1 - MT healer
Healer 2 - Raid healer, must be capable of keeping MT / OT up as well
DPS 1 - Hunter by preference
DPS 2 - AoE by preference
DPS 2 - AoE by prefernce
DPS 4 - Shaman by preference
DPS 5 - Shadow priest by preference
DPS 6 - Open slot
This structure resmbles two 5 man groups more heavily, yet is far more structured, with a shadow priest and shaman being in the group by preference for their mana regeneration and healing capabilities as well as the benefit of Heroism. Again of course this isn't the group everyone uses, its just rather common. This is where issues start to appear, while you don't overgear the instance and the timers that forming 2 groups like this from a generic 25man is hard, and even if you can there are 5 people left out of the run. Most guilds I have been in, well both of them, and most I know of can put together at least 1 Zul'aman group, and that group often will push 2,3, and finally the 4th timer, while they are working on the 2nd timer there are few issues, most other people in the guild are supportive, yet would rather not spend the time, money and consumables required to make it work. As the 3rd and 4th chests however become viable the guild begins to see the group running as being "elitist", "discriminating", or at worst "forming a clique", that this group took the time and effort to run and was formed often by random "who wants to go ZA" announcements is disregarded, the progression seen, and the lack of progress in a 2nd group (often due to lack of experience, ZA on the timers is horribly unforgiving) acts as a further demotivator.
The introduction of timers, and the 10 man nature, both act as horribly divisive points in Zul'aman, how do you integrate it into a guild, and the progression within it without dividing your guild and creating bad feeling amongst people who normally raid 25 man instances together. This is the point I am unsure of, I like the timers and the smaller nature of the instance, its fun, its challenging and those timers hold your interest as a "progression" instance far longer than Karazhan ever did, where clearing it once often became "farm". Yet working backwards and creating a timer capable group is showing elitism and forming a clique, it might not be in the traditional sense, after all you are merely forming a group the way the instance requires at that gear level (such as a mage tank on High King Maulgar). I suppose its something that needs to be thought about, a purely 10 man progresssion is a great thing for the game, it lets guilds that can't cross that boundary progress, and it lets guilds that can see the fights on a smaller scale, and have a different experience on the fights in a similar way to the 2nd boss of Magister's Terrace does. However I think in the future purely 10 man instances need to be thought on more, and to find some way to integrate better with 25 man guilds, without it many guilds will suffer from seeing this otherwise very fun instance.