I just killed Chogall this week with a 10-man group.
And then, I remember... Naxxramas. The bosses in Naxx, how do they compare with the bosses of T11?
How does Chogall compare to Kel'Thuzad?
I think Chogall is more difficult. In a way, it's hard for me to guesstimate because of how late I started raiding in Wrath, having only been level 65 when the expansion hit. I learned KT when lots of other people were already doing the fight.
With Chogall, I had to learn it with the group. But, there are some nasty things that Chogall makes us do. Worshipping, both my 25 and 10 man groups had trouble with this. I admit, I'm not very good at interrupting because I normally don't need to in a raid setting.
The new Power Bar for fights like Atramedes and Chogall are an interesting new concept. In a way, it's not new, except that I have a feeling we'll be seeing this mechanic in various forms throughout the expansion.
But how does Chimaeron compare with, say, Loatheb? From the healer standpoint, they were both gimmick fights. Stand around twitching for folks about to die, spam heal once every XX seconds. Massacre is like a strange inverted healing buff. I didn't mind Loatheb, but Chimearon feels too gimmicky for me. I hardly ever use Flash of Light. I feel like Chimearon's sole reason for existence is that I have to use it this tier.
And lastly, remember dear old Sapphiron? I'm glad that so far, in Cataclysm, there have not been many dot-auras. I don't miss them, especially now that we aren't set up for them. Yet, in Atramedes, there's a very cleverly disguised dot-aura. Instead of ticking every second, it ticks once every few seconds (Modulation). Players with low sound take a little, players with high sound take a lot. I actually like this fight. If executed properly, it's pretty easy and there's still a lot going on.
We raided ICC for fun, and to get the LK down (a guildie just got his legendary, we'd only needed one more kill to get the neat quest items). It was a bit strange to be back in ICC, I kept trying to play like it was still 3.3. I really hate to QQ about how much better the old days were, but, I don't recommend letting yourself forget that Beacon only transfers half.