There's not much I can say about this film that hasn't already been said by a multitude of bloggers, none of whom said it better than Jeff over at Conditional Axe (née A Love of Great Trash). If, however, you crave a disssenting opinion, then may I direct you to The Explosively Talented Christopher Bird, whose critique is well-written (however incorrect and foolish it may be).
Though I mostly agree with Jeff, I want to make one point: this should not have been the third movie. I truly, deeply feel that this script, and that of POTC 2, should have had major surgery done on it to turn it into a single movie -- Pirates of the Caribbean: Davey Jones' Locker.
I hate, Hate HATE movies that have an incomplete ending, even when I know there's a sequel coming out the next year. HATE it. I see it as a sign of storytelling weakness. And so, to my mind, Dead Man's Chest is only redeemed by virtue of At World's End tidying up the plot strings.
So if you do plan to see it, here's my suggestion: watch POTC 2 again, and when it ends pretend that it's actually intermission. Then go see POTC 3. Trust me, it'll hang together a lot better and feel far more complete.