Not that it's some sort of extreme accomplishment, but 10 man Naxx = completed.
We also, as a guild, took on 25 man Archaevon with just 20 people, most of them fresh 80's in blues with just 3 healers. Archaevon enraged on the first attempt, hitting all of us with a warstomp that instagibbed the entire raid. We were 8 seconds from enrage on the second and final attempt.
I don't mind the (essentially) free loot, but seriously, shouldnt there be -some- hard bosses in the first tier of raiding? I haven't done Malygos, yet, but I can't imagine it to be that much more difficult than anything else I've seen. Maybe it will be hard with the nerfed CoH. Magtheridon and Gruul, even in their current fixed state, are harder than Vault/Naxx. Hell, even Nightbane is harder.
Honestly? I'm looking forward to Arena Season 5. Playing a Priest should be quite difficult in this world of uber melee, no resilience and sick nasty burst.