For me my favorite moments aren't even necessarily the fighting parts, although the trash waves with the healing totems was kind of fun for me (so much AoE) - I really almost wish I could tag along the raid and simply look at everything. Making the trek through the Vale, and then into Orgrimmar, there's been a lot to see so far, some really fantastic work has been done to take familiar elements and make them new and distinct for the raid. The hints dropped back at the beginning of Mists about Ragefire Chasm have come to pass, and its pretty amazing to get to see it.
So, now it's your turn. What do you think about the Siege?