Today I hit 80.. and headed over to Utgarde in mostly S4 gear.. and went in with a Warrior in decent gear.
All in all.. not very hard considering my poor gear. Definitely a challenge. Requires a lot of focus, especially the healing. Make sure you use at least one Hex on the humanoids and the beasts to make these pulls safer.

The bosses and my experience:

Svala Sorrowgrave
Not hard. Just tank and spank, basically like normal but with bigger hits (you read something else?..).
Wipes: 0


Gortok Palehoof
The hardest actual boss fight in the instance in my opinion.This is a DPS race against his stacking debuff.. By the time we were done, my shaman were at 5-6k hp and were almost one-shotted by his random damage. Extremely tight. Increasing your DPS will surely make this fight easier.
Tip: Make sure you heal the impaled character quickly.
Wipes: 2


Skadi the Ruthless
Pretty tough prelude fight - lots of opportunity for you to screw up and die. Park your box team by the harpoons and have the tank+boss down the corridoor, so that the whirlwind can be kited properly.
Tip: Be calm, take it easy, regen mana before you activate the boss.
Wipes: 4

King Ymiron
Not very hard, just requires you to focus a lot.. one mistake and it's downhill.
Tip: Put down healing stream totems after the first boat - chances are that you will be taking some team damage. It will also make your tank survive longer when you need to kite the "orb" that can easily kill you in seconds.
Tip: Purge his buff immediately.
Wipes: 2