So far it's been easy. Plain and simple. When I say "easy" here is what I mean:
I had the impression that it would be more challenging then 10 man. It, so far, is absolutely not. (Given OUR team which has a lot of naxx 10/heroic loot/epic rep/craftable/badge loot geared ppl) At least 10 of us have naxx 10 on farm and have almost all the best gear from there. Plus, some in our group have 25man loot and experience. And we have very skilled players on a multitude of lvls. Some are better mechanicaly, some are more knowledgable etc etc. We killed the second spider boss with a full enrage from start to finish and got the achievment. I'd say we are geared.
We did get a bit cocky/overconfident which lead to a little carelessness on the blob/trash room that cost many wipes. (Some of that was not knowing how fast the trash respawned though) Other of it was simply not being together/ready.
The challenges I see:
Hegien (With 25 ppl) While our 10 man group has that down with no deaths (most of the time). Not sure about others in the 25 man group.
Thaddious, more complicated with 25 ppl. If a few don't shift to the correct side during polarity, it will cost us. However, a simple, non-complicated explanation of that fight does wonders. It's actually very simple. As far as dps goes, blow all specials, trinkets, heroism. (And like Adam said, try to be prepared) You will feel better knowing you are contributing to the group and are being considerate of others.
KT, more complicated on 25 man.
(By the way, our healing and tanking is very good. All of those ppl are in epic gear.)
Rhys you brought up potential dps issues. That includes your toon right? (Which did about 1.7% 1600 dps) Because it is true patchwork was a bit of a strain on mana last night, because of some low dps. We were throwing inervates around.
But for last night, that's ok. Our goal last night was to get 25 guildies together to test the waters and over all It was a fun "casual" run, meaning we were able to bring all forgiven ppl, some geared, some undergeared. However, some of the ppl who plan on staying may have to work on their gear some to manage certain fights. (Makeing them doable and or less risky)