I have been playing a game a Palermo to put the Sword of Islam DLC through its paces, and i am pleased with it so far. I would definitely say it is worth some money. I may not quite be ready to say worth $9.99, but i have yet to see all it offers.
Palermo is not a wonderful place to start as a Shia ruler. You are basically surrounded by rulers with sweet, sweet Holy War Casus Belli on you, and they aren’t shy. You of course have the same options to use against them, but unless you have managed your alliances wisely (cough Egypt cough four wives cough), you aren’t going to have the necessary muscle to fight off the extra six countries who come to their defense.
But you don’t have to sit and wait for you Vizier to fabricate claims either.