Inherently, the story of this raid is more complex for the Horde. The Alliance has always had to deal with brutal Warchiefs: Blackhand, Orgrim Doomhammer, and now Garrosh Hellscream. But Garrosh's acquisition of the Heart of Y'shaarj both gives them a reason to shift their focus away from the various battlefronts and go for broke, taking down Hellscream as quickly as possible.
The Horde has seen things slipping farther and farther into a kind of fascist totalitarianism ever since Garrosh took charge, but his assassination attempt on Vol'jin was the real catalyst for change. His treatment of the Trolls bodes ill for any of the other "lesser" races, and we've seen him alienate the Blood Elves and Goblins. On one hand, the other Horde races want a strong Horde that can take what it needs and not need to fear outside forces, but Garrosh has made it clear that there is no place for them in his Horde. Even if you were a die-hard Horde zealot, if you're not an Orc, you know that things aren't going to work out for you (and if you're an Orc Warlock, you're in serious trouble.)
But the raid! Let me get to the raid.
Siege of Orgrimmar is a huge instance, divided pretty neatly into different segments.
Vale of Eternal Sorrows:
This first part of the raid is almost like a small mini-raid that in the BC days would probably have just been made a separate instance. The fights here are a little more intuitive and tuned, I believe, to be easier, but there are some clever mechanics.
Immerseus is an effective gatekeeper boss: simple, but with high enough damage and DPS requirements that it sets a bar for what kind of gear you're looking for. First bosses should be simple, and I think this one works out great. Plus, what a cool model!
The next segment of this wing has us going through familiar territory, which is always a fun thing to do if done in moderation. As you'll see, I think this raid strikes a pretty good balance on the familiar versus the new. Likewise, I appreciate that in the two 4-boss wings of the instance, there is no trash between the first and second bosses. Trash is important for setting a pace (Trial of the Crusader showed us that,) but given how long four bosses can drag, I think this was a good choice.
I do think that the Norushen and Sha of Pride fights were a little too similar in style, but they both had their interestingly unique aspects. Norushen obviously requires a certain degree of individual responsibility. Sha of Pride also has some tricks, but I think it ultimately boils down to being pretty much this raid's most Patchwerk-y fight (even if they said that about Malkorok.)
Anyway, this section of the raid provides a good answer to why we've picked this moment to take down Garrosh. It also introduces (through the Fallen Protectors) a big theme of the raid, which is that we're killing a lot of people we've known for a long time.
Gates of Retribution:
This section of the raid is really what we were all thinking of when the idea of a Siege of Orgrimmar was put forward. The entire wing takes place in the city we're familiar with (though the last part is in Ragefire Chasm.) Galakras is a pretty exciting first fight, and also emphasizes a mechanical theme for the raid, which is the importance of fighting adds. It's also fairly enjoyable to do one of these fights where the raid splits up, even if you're only going to the top of some towers. I do feel that Zaela doesn't really get the send-off she deserves, as she seems to simply fall to her death from atop Galakras. Zaela was likable, and while it makes sense she sided with Garrosh, we didn't really get to hear much from her until we were fighting her people.
Iron Juggernaut is pretty conventional as a boss, as are the Dark Shaman as a kind of smallest-possible Council fight. Clearing out a bunch of familiar NPCs from the Valley of Strength (including the bosses, who were two obscure Shaman trainers) is pretty cool, though some of the shopkeepers feel like they ought to have been hiding. And then of course, you face Overlord Runthak and free Gamon before facing down Nazgrim.
Nazgrim is of course the most heartbreaking fight here, because he makes it clear that he's only fighting for Garrosh out of a sense of duty. Mechanically, it's yet another add-focused fight.
Here's where we get what really feels like a conventional raid instance, though it's also not so overblown in size as to seem unreasonable as an actual fortress. This truly feels like a military base as you first assault it. Then you come to Malkorok, who gives us our first taste of something otherworldly in Orgrimmar. Malkorok is kind of an interesting fight, though I imagine it's most bizarre for healers. You also of course have to play your little "memory" game with it, but it's a fight that's mercifully devoid of adds after the last couple fights.
And then there's Spoils of Pandaria. Spoils is probably the least conventional fight of the instance, but like many of them, a lot of the individual mechanics of the adds kind of get drowned out by the frantic and chaotic nature of it. I enjoyed Thok the Bloodthirsty quite a bit, mainly due to the perverse humor of freeing all those prisoners only for him to eat them. Thok is one of those great, classic enormous bosses: simple, yet dangerous.
I have yet to see Siegemaster Blackfuse as DPS, but what I can say is that it's pretty fun to tank. Any time a tank gets to do significant damage and kill something on his or her own is pretty exciting. Plus, I'm a huge fan of the weird kinds of technology that they have in WoW, and this fight is all about that.
After Blackfuse, you kind of make your way out of the really conventional military base part of the Underhold and you start going through tunnels. I'm not quite sure where you are at that point, but it's probably not Orgrimmar anymore. The Paragons of the Klaxxi are kind of interesting as a penultimate boss, though I imagine that the difficulty of the fight largely depends on the luck of what order you get. On its lowest difficulty, it suffers, like Spoils did, of having a kind of mechanical overload - one sort of just ignores the mechanics because there are too many to keep track of.
Finally, there's Garrosh. Garrosh actually surprised me in that it's not that hard of an expansion-boss fight if you know what to do, and the mechanics can be broken down and pretty easily understood. However, I do think there are some pretty cool unique mechanics, particularly the visions. The Garrosh fight would be pretty mundane in visuals if it were not for the visions, but every time you get sucked into the Heart of Y'shaarj, you get to see a bit of the connection between the super-familiar (Garrosh and his "True Horde,") and the unique stuff of Pandaria.
Finally, I think the two cutscenes: the Horde showing Thrall stepping aside for Vol'jin and the Alliance one showing Varian making a decision to end the war, do a good job of establishing the new status quo going forward. Add on to that the fact that we get to talk to many of our leaders (no Genn or Velen though, boo) and see what they think of the situation, plus a whole mini-quest chain involving Lorewalker Cho and seeing how Pandaria is going to move on, and you've got the most story-driven raid yet.
Mechanically, I think we've got a fantastic raid in Siege of Orgrimmar, even if it leans a little heavy on one standard mechanic (kill these adds!) It's a fitting way to end the latest great war between the two factions, and it leaves a ton of questions that will have to be answered in the future (like who is still alive in Orgrimmar?)
So that sums up all the raids in Mists of Pandaria. In the future, I'll be writing up an article about the relationship between Raiding, Dungeons, and Scenarios, and how that's worked out in Mists.