Well, let's see...
The new professions. Dervishes now have the most powerful weapon in the game. Their builds focus around using Enchantments and, most often, status conditions. Three of the popular builds for GvG use Avatar of Grenth, Ebon Dust Aura, and Avatar of Melandru. Paragons are obviously used for support - one of their skills, "Incoming!" has actually been nerfed already. You don't really see them much anymore with that gone. Sometimes you put them in builds with Searing Flames eles to compliment the Burning.
Hero's Acent is now 6 vs. 6.
You can't mix dye anymore. Also, it shows what the new item will look like before you apply the dye. There are new dyes, too: Brown and White. Grey Dye has replaced Dye remover.
After the next ladder reset, the GvG is going to have a whole new rulebook. It's going to be more "tournament-based." So, after this ladder reset, the ladder is never going to be reset again. In fact, there won't even be a ladder. Read more about it on
www.guildwars.com, I don't know all that much about it.
That's about all I can think of for now. I'll post more if I think of anything else.