So, this is my own personal Utgarde Keep guide. I'm sure there will be other guides, and I'm sure you can find the info elsewhere, but hopefully, I can help you out and get you ready for the Keep.
First and foremost, my initial impressions: I love the spacing of the instance. This relies less on pulling skill and more on group skill. You won't get too many mobs unless you try to get too many mobs. The instance in itself is absolutely beautiful. Just gorgeous. I cannot say this enough. Blizz has hit a home run with Wrath. Its better than I could've imagined.
Now, there's two quests you can complete in Utgarde, which are very easy to get. There's a guy just north of town on a small hill who tells you to go meet up with a guy just outside the instance, who gives you two easy quests to complete. Don't worry if everyone in your group has the Weapons quest, there's plenty throughout the instance, enough for all 5 of you to get 5 weapons each.
Onto the guide...
The first room is a large circular room, where the mobs come in packs of 3 or 4. Personally, I decided to down the casters first, and go with no CC. If you do choose to CC, the casters are probably the best target. The annoyances tanking these initial packs are caused mostly by the spear throwers. They love to stand just out of melee range and toss spears at you. Not a big deal, until they start throwing spears at the healer or the warlock. What I did was charge the caster, then walk the mobs over to the spear thrower, thunderclap, and shockwave. Worked very well, and after that, our aoe crew could open up at will.
The second set of mobs are the proto drakes and their trainers. These drakes have a pretty nasty frontal-cone aoe, so don't pull them next to your healer and ranged and aim them that way (unless, of course, you love torturing your healers....) I had issues with seeing the trainers as they sort of were eaten up by the Drake's model, and the drake's have a really small hit box for something so big.
Then you come to the room with the first boss. Things you don't want to do here?
Charge one of the 5 mobs in the room (which includes the boss). You can pull the 4 separately, deal with them, and then engage the first boss.... which I didn't do the first time, because I was just marking and rolling along, talking about how much I enjoyed the instance and it didn't really register in my head that the named was a boss....
The first boss is an interesting one. She periodically summons mummies to beat on everyone, they have very low hitpoints, and for me, a quick thunderclap and they were glued to me and beat themselves dead on my damage shield. The other thing the boss did was entomb one player in an ice block (similar to Demon Chains from Illhoof). To combat this, our ranged would switch over, and if it was our healer, I would charge the ice tomb and hit it a few times (shield slam is nice here), and then go back to the boss.
Moving forward from the first boss, there was a set of undeads tell your casters to hold back, because the little geists can make quick work of a clothie, even though they hardly have any hitpoints.
Keep on rolling through more 4-5 pulls and you'll soon be upon the second boss. This might be my new favorite fight, and as a warrior you can really make it a lot easier on your group.
Now, what happens? The two mobs need to die within a few seconds of each other, or else they will rez and you need to start all over (think Romulo and Julianne, you Kara vets). I had my groups beat down the melee mob to about 25% or so, and then switch over to the caster (I was tab targetting to interrupt the caster from casting while we beat the melee down). Burn the caster down, and the melee should've beaten himself almost dead on your damage shield, and finish him off. Baddabing, baddaboom... phat lewtz.
(Wow this is getting long)
More trash, of the same variety, eventually you get to one new mob, a Drake with a mounted rider (reminded me of the Bears in Zul'aman) just before the last boss.
The last boss is... well... a challenge if you aren't Kara geared (at least). He has a few skills: A spell called Smash, which does 6-7k on plate to anyone within melee range (run out Rogues, Ret paladins, fury warriors, save your healers the mana), and an aoe silence (so have your last stand and shield wall ready, just in case). Once he dies, he ressurcets to an undead zombified version of himself, and proceeds to beat you down with even more of a can of whoopass. He has two aoe's which get stronger (3-4k with a big range, and 8-9k for those in melee range).
So, this is a healer fight, love them, hug them, squeeze them if you survive it.
Posting this now, will (hopefully) add pictures, and corrections later on today!