Not to say Pirates III completely sucked. I enjoyed it, it was just disappointing. I completed the trilogy and will probably have to buy the DVD just to complete my set.
Jack is still Jack which is always a plus and I did enjoy the quadruple double-crosses they had going at one point. By the time Keith Richards showed up, I had completely forgotten he was going to be in it. He looked perfect, played his part perfectly, the director made him comfortable and did not ask too much of him. Heh. They probably didn't bother with any makeup for him.
If you do go, it's very long, so don't drink too much before hand and stay for the end of the credits. Unbeknownst to me, all 3 movies have a final scene at the end of the credits and I missed this one as well. I'll have to check my DVDs for the others.