Here's my favourite instance. It's short and sweet while the bosses are interesting enough that you can't really fall asleep on it.
We begin our trip at General Husam who has three main fight mechanics. Firstly, he will periodically pick up random players and toss them at the nearest of two pillars in the room. Healers will need to be aware of this and throw some quick heals at the target of this attack because they will be taking damage from the hit and then subsequent fall damage. This is the only non-avoidable source of damage for DPS and Heals on the fight and the ability of these two roles and the Tank to manage Husam's next two abilities will determine whether you're going to kill this boss or run your Healer out of mana in short order.
The simplest of the two remaining abilities is Husam's Shockwave attack. Similar to the Frost Giant from Nexus in LK, Husam will announce this attack, stand stationary and send out ground waves that shake the earth and spread away from him in the form of an X centred on himself. Don't remain standing on this ground - moving into the gaps between the X - because a few seconds later it's going to erupt in waves of spikes.
The one you need to be more careful of are the traps he will be periodically throwing down around the room. These Mystic Traps are brown circles with pulsing yellow centres - looking kinda like, and henceforth refered to as, Lemon Fruit Cremes - you want to avoid standing on these whenever possible, particularly as melee, because they will knockback anyone in their blast radius (which, like the mine field in Storm Peaks, can have really bad chaining side effects if you're unlucky), and do noticeable damage. Occasionally Husam will cast Detonate Traps and these Lemon Fruit Cremes will start emitting large yellow circles around themselves. At this point, you need to clear yourself from these circles - quickly - because they're going to explode and hit anything within their radius. While one is survivable if you're at good health, finding yourself in two or more of these Traps blast radius will basically one shot you and eating even one is going to consume a decent amount of healer mana to patch you up. So, when these start glowing you should be looking for a safe place to stand and getting there.
A couple further notes for the tank on this fight:
1: Somehow the idea got out there that it's a good idea to try and "pillar hump", as they say in Arenas, with this boss. This is a bad idea because it does two things that make the fight much more difficult than it need be; frequently Line of Sights your healer so they can't patch you up easily or efficiently while chasing you around and, even worse, ends up dropping Lemon Fruit Centres all around the pillar you're humping. That last one quickly becomes fatal once the boss starts throwing people at the pillar and they begin landing.... on a pile of mines. Don't do this and, in fact, considering that point you should maintain some distance between the boss and pillar instead.
2: Once you're comfortable with the fight, you really don't need to kite him constantly nor, really, all over the place. Learn to watch for how heavy the mine concentration around you is getting, whether or not the melee have room to work around him, and whether you can exit during the detonate phase without having to run through a ton of mine zones yourself. By moving with judgement and keeping the boss more stationary, your caster DPS and Healers will be able to work more efficiently (from both a DPS and Mana standpoint), because they're not forced to chase you around casting instants.
Next on this adventure is Lockjaw and Augh. On Heroic this is a two part fight but on either mode you can cheese the mechanics for the Lockjaw part (for the moment at least), by having everyone standing atop the two Crocodile statues at the far end of the room. This completely mitigates Lockjaw's primary mechanic Scent of Blood which places a bleed DoT upon a player and causes periodic spawns of little crocodiles to seek out that player and start chomping on them; doing both bite damage and increasing the strength of the DoT. While you'd traditionally have the target of that attack move to the tank so he can pull all these adds off them, by standing on the Crocodiles the adds will simply stand at their spawn points and twiddle their thumbs and can be completely ignored. That said, standing up there until 20 spawn and having melee drop down to pull the adds over for everyone to AoE down is also the easiest way to get Acrocalypse Now done if you're chasing achieves.
During the Lockjaw part, Augh will periodically throw a poison dart at a random player and whirlwind through the room. Dispel the poison DoT from the dart ASAP if possible 'cause this is cheaper than healing through it and, as usual, don't stand in the Whirlwinds. If you're fighting Lockjaw on the ground, Melee should also be aware of his Dust Flail ability that throws up dust to his rear, doing both damage and reducing your chance to hit while in it.
At 25%, Lockjaw will enrage. Tanks/Healers should be prepared to use cooldowns here to keep up with the damage but Druids can Soothe this enrage off and should do so where possible to make this phase more manageable; especially if you're juggling the adds. Presumably other classes that can cancel enrages can do so as well.
Once you kill Lockjaw on Heroic, back away from the Temple entrance towards the stairs down into the area because now you're going to have to fight Augh and backing off will give you time to heal up and drink before pulling him. This is essentially just a tank and spank phase as Augh is really simple. He will periodically start whirlwinding towards a random target: run away. He'll keep throwing Poison Darts at people: handle as within the first phase. Finally, he'll periodically smoke bomb, stunning the melee and making him harder to hit while in it: move him out. Wash, rinse, repeat steps, collect loot.
Our third participant at this party is High Prophet Barim. He's mechanically simple but is a pretty solid Healer and DPS test because of his second phase. To open, you're going to Tank Barim while he executes two primary mechanics. Firstly, he's going to pick a target and cast Sun Fire on them. Don't stand in the flashing light. Secondly, he's going to spawn a Phoenix that does AoE damage to anything in proximity as long as it's up. Because of this, it's best to have Ranged kite and "kill" this mob. I say "kill" because what will happen is that that the Phoenix will return to it's egg and keep healing. At this point, you can either damage the egg to keep it from hatching again or go back to the boss. To be honest? Just go back to the boss. His final minor mechanic is Plague of Ages, a disease DoT that will hop around the party if not dispelled away from everyone.
At 50% Barim's going to start his second phase by stunning everyone, spawning a huge white circle, sucking everyone into it, and then throwing everyone away from him (and out of the circle), into a Shadow World. Note one: this huge white circle is now a void zone; don't go back into it. Note two: Barim is now no longer attackable until you kill the Harbinger of Darkness shadow Phoenix that will spawn to exit the phase. Sounds simple, right? Well... it is as long as you're geared well enough to manage the rest of the mechanics here.
Firstly, as long as you're in this phase you're taking AoE shadow damage so you want to kill the Harbinger as quickly as possible (the DPS check), to keep your healer from running dry (the Healing Check). Complicating this is everyone's favourite mechanic from the first boss in Forge of Souls: people spawning shadow images of themselves that empower/heal the boss if they get to them. This time called Soul Sever, the target of this will get a nice purple V arrow on their head and will shortly spawn the add. If these adds reach the Harbinger they increase it's damage output by 20% each time which will quickly overwhelm the healer if you allow too many to reach the Phoenix. There are two ways to deal with this, either kiting the boss away from these or nuking them quick, and how you attack it is really up to you. Although, if you're finding that phase is taking too long you may find that you've no choice but to kite and keep DPS on the boss as long as possible. This phase is also a good time to Hero/Bloodlust/Timewarp if you're having problems getting through it. Although, you should be aware that you'll be either waiting or denying yourself the ability for the last phase of Siamat if you do. Finally, the Harbinger will periodically spawn ground fire. Don't stand in fire.
If you can successfully clear this phase by killing the Harbinger, you'll be pulled back into the "Real World" by Barim and can finish him off in what essentially amounts to a repeat of Phase 1.
With Barim down, you move directly to the final boss of this instance: Siamat. An even larger DPS and Healing check than Barim, Siamat is a two phase fight as well.
To open, Siamat will shield and spawn three waves of adds consisting of one to two caster adds (Minion) and one melee add (Servant). Tanks should prioritize picking up the Servant as quickly as it spawns because it hits hard. DPS can pick up the Minions, who don't melee for much, and kill them quick while staying spread out because they will chain lightning the party; this cast can and should be interrupted as much as possible to minimize incoming damage. You should also try and kill Minions off to the side because they will spawn green whirling void zones where they die. Servants are interesting on heroic because they cast an ability called Lightning Charge as they die. This ability does moderate damage to any one it hits and places a buff on them that increases their damage done by 10% and haste by 10% but also increases their damage taken by 33% and can stack 3 times. While this can make life on this fight much easier from a DPS standpoint, it's going to make life hell for the Healer in phase 2 because Siamat is going to start chaining energy streams on everyone. How many stacks of this you want to pick up, if any, largely depends on your Healer's ability to get through the increased damage taken in phase 2 and whether or not your DPS can compensate regardless.
Once you get through the three waves, Siamat will drop his shield and the final phase will begin. this is a straight up burn phase with a couple things too consider. First, as mentioned, Siamat will begin casting Palpatine-esque lightning at everyone in the room which establishes the soft enrage for this boss - you must kill him before your Healer can't heal anymore. Bunching up for AoE healing would be optimal but, complicating this, is that Minions will continue to be spawned throughout this phase and their Chain Lightning will add to the damage output. Kill them, remembering to do so away from the boss and/or to move the boss away from the void zone that will spawn when the Minion dies as well as to interrupt that cast as much as possible. If you let these Minions run wild, the combination of their damage and Siamat's will run the Healer dry very quickly so, as much as a priority killing him is, don't forget them; especially early into the phase and definitely so if you've let the Servant buff stack to 3. You don't want to be getting chained from Siamat and the Minion with a 100% damage taken buff on yourself.
All that said, execute appropriately, and you'll quickly find Siamat lying before you with sexy loot for you to wear as you head for the door.