With all the bosses now out I'm thinking back over the dungeon and putting the bosses in a logical order.
Personally I prefer 25-man raids so my specific list will only be for 25-man difficulty. Others can surely comment on 10-man.
25-man Icecrown boss difficulty ranking
#1: The Lich King is easily the most difficult encounter in the zone. Not going to say anything more until I've killed it.
#2: Sindragosa isn't really any harder than Putricide or Lana'thel until she hits 35%, but her soft enrage is an extremely hectic phase. This encounter is markedly more difficult than the other wing bosses in the final phase, Putricide phase 3 is pretty tame compared to this. Keeping up with everything thrown at you and still DPS-ing Sindragosa is a big challenge.
#3: Blood-Queen Lana'thel is probably slightly less theoretically complex than Professor Putricide but the DPS and healing requirements are leagues higher. She turns into a monster going from 10 to 25. The air phase is hell to get everyone alive through on 25 and if anyone dies the enrage is a huge threat.
#4: Professor Putricide is an encounter that requires a fair bit of learning and he's definitely not too forgiving just not on the level of the other end wing bosses. When it comes down to it his DPS and healing requirements are low enough to give you leeway in screwing up his mechanics. Random crap like abilities hitting rooted players are annoying but you can have someone die and still be okay.
#5: Blood Prince Council: I've changed my mind on this, this encounter has a lot of points of failure that will just instantly wipe you, two Kinetic Bombs going off or Keleseth tank dying or a fire sphere hitting a bunch of players when the target is slow. There's a lot going on and it's more to learn than any of the other non-end bosses. The DPS requirements are very low however.
#6: Valithria Dreamwalker seems like a encounter that walks a very fine line of tuning. If your healers don't lose their dream stacks and your DPS keeps up with the spawns this will seem very easy. If you get behind at all or the healers lose their stacks getting overwhelmed is just as easy.
#7: Rotface seems more and more to me like a fight that is entirely reliant on a fast DPS burn. The mechanics are very simple, kite an ooze around and run to it when you have a debuff. Move a bit when it explodes. This encounter isn't too bad to learn at all, it's just getting the DPS you need. As your DPS increases this becomes incredibly simple and the healing load much lighter.
#8: Festergut is a gear check. Easy to learn and easy to execute. If you're wiping on this your gear is terrible or you're not playing well.
#9: Deathbringer Saurfang got buffed this week but he is still relatively easy. A decent gatekeeper for the rest of the dungeon.
#10: Lady Deathwhisper used to be harder than Saurfang but after the nerf not too bad at all. Lots going on but the tuning is incredibly forgiving.
#11: Lord Marrowgar exists to be slain for a raid weekly these days, and also to not drop whatever you need.
#12: Gunship battle is just Yeah.
Your thoughts and opinions on the instance?