I cannot put my finger on what it is exactly that is missing, but it failed to ignite much of anything for me. I failed to stir for any of the introduced characters and I came away with the uncomfortable feeling that the church was pulling it's fingers out of a cookie jar somewhere.
Yet, that's not to say that I entirely disliked the movie for I love the world of Jack Sparrow and am quite content just to simply be there even when nothing much is happening (much like some of the WoT books, eh?)

I have a feeling it may be missing much of the humour of the others. Many of the scenes were predictable, and the sword scenes went for far too long without variation. Wongy Jnr said it was full of too much "boring bits" that "dragged on too long"; however he liked that he could understand the storyline with this one in a way he couldn't with 2 and 3 (having only just watched the first three movies this week).
And Penelope Cruz? I don't see what it is in her character that would spark an inveterate womaniser's feelings, other than the very obvious push to make her a female version of himself.