We finally ventured into Onyxia's lair last night and had a fun time reliving that all over again. I am tremendously upbeat about Blizzard revisiting old content like this--even ahead of Cataclysm. There are many people who never played during Vanilla WoW, and it constantly amazes me when I see guild members, or random strangers asking about this instance, or that encounter. Even in our raid last night there were a handful that had never raided Ony, and had never been to Molten Core. Such stalwarts of WoW deserve their time in the sun yet again.
The fight is nearly the same as it was in Vanilla, so she should be as much of loot pinata as she ever was. One warning however--I found it simply impossible to hit her in phase 2. I tried many times at various locations under her and couldn't hit her regardless of what I did, which means groups will probably want to ensure they have enough ranged DPS to bring her down so phase 3 can begin.
I got the 22-slot bag incidentally.