I've written about the lower tier of bosses before but since we've seen most bosses on heroic now, I think I have a better gauge of the difficulty level. Last night, in about 3 hours we were able to clear 5 heroic modes and worked on 2, and gave up on 1 just to keep going.
Anyway - if I were going fresh into ICC, here are the bosses I'd tackle on Heroic in order. Each list goes from easiest to hardest in its block.
EASY: First time in, I'd focus on these five, though I could skip Marrowgar, he can be a bit finicky until you learn the rhythm of the fight and H:BQL is a moderate DPS gear check but really shouldn't be an issue at this point. These are bosses most groups can consistently kill every week, I think.
- Gunship (What is this. I don't even.)
- Rotface (3 healers make this easy, ranged stay at, uh, range, and avoid the puddles.)
- Festergut (If 5 of your DPS can beat the enrage timer, 3 healing this makes it very easy.)
- Marrowgar (3 heal this and coordinate the Bone Storm park locations on tanks, everyone else stack in the middle and kill spikes.)
- Blood Queen Lanethil (Just a very strict DPS gear check. Tanks will take increasing damage as you make more vampires, otherwise it's the exact same fight.)
- Dreamwalker Valethria (Remind the healers to heal themselves while they collect stacks, tank the blistering zombies, and if you can, solo tank and go with 4 healers to make it go super fast. Tanking this is fun. And will give you an ulcer.)
- Blood Princes (This is a stupidly long fight just because your ranged will spend all their time juggling kinetic bombs who drop very fast and take a lot of focus to stay juggled. 3 ranged make this a lot less complicated, and 3 healers give you breathing room, 3 tanks will also make this less stressful which leaves you.... one DPS killing the bosses full time. Better geared teams might be able to get away with 2 healing this. Shadow Prison is a bitch. Just make sure people stay spread out for Empowered Shock Wave, that bombs get juggled, that targets of Empowered Flame Orbs get absorption shields and kite the orbs, and you should be fine.)
- Lady Deathwhisper (lots of new mechanics make this challenging - phase 1 more or less the same, just kill the Adherents first their bubbles are stupidly powerful. Taunt immunity and Mark of Insignificance make phase 2 very interesting with incoming adds, actually dangerous ghost explosions and Mind Controls. Having two rogues (or two hunters, or a rogue and a hunter...) makes the threat thing a non-issue. Make sure DPS sit on their hands, use their own threat-drops, and get Hands of Salvation from paladins. Fun fight!)
- Deathbringer Saurfang (2 heal this if your DPS is good enough to kill him before he gets 3 marks out, otherwise use 3. Paladins are OP healers on this fight. Add-kiting and killing is actually challenging if you don't get slows/stuns on them. I am thinking of swapping my spec around for this fight just so I can guarantee stuns on every add-wave.)
- Professor Putricide (the two-add transition is not that bad, but juggling the unbound plague is what makes this hard.)
- Sindragosa (haven't spent any time on this yet, and while the exploding unchained magic looks like it's challenging, the real threat on this fight will be her massive health pool and whittling it down before her enrage while coordinating phase 3 and the unchained magic.)
- Lich King (I don't know if our 10-man geared guild can kill LK yet - I see one guild in strict and small handful on casual progression having pulled it off worldwide, and our last buff to ICC comes in a couple of weeks so we'll see what happens then, but I'm not holding my breath. The super-strict comp (which we can actually meet!) and gear requirement makes me doubtful we'll get this but I do want to spend some time on him.)
Here's hoping I'm right for once!