The short version of my review: it sucked. Not as badly as #2, but that's really not hard, since the second was a 2-hour trailer for the third.
Now the longer version. It was nice to see some of the various storylines coming together, but the missing element in all this was the interests each of them had in their...whatever it was they were doing (mostly screwing each other over - and btw, spoilers ahead). It wasn't clear, for example, why Orlando wanting to save his father necessarily goes against Keira Knightly. Or what the hell Jack Sparrow was after (immortality? legendary status?). As a result, you didn't get the banter or witticisms that came from Jack playing off all the characters against each other in the first and to a lesser degree the second.
Action was fine, and there were some really cool shots, but the lack of motivation for the characters really inhibited things. I think a big inhibiting factor is that no one has really ever made a successful naval battle shine on the screen (please correct me if I'm wrong, as I'd love to see it). It all boils down to what happens on deck, or in the tight framing of two ships going at it, but you don't get the grand sense of what's happening in the wider battle. Truth be told, this is probably the case in larger land battle films, but the particular nature of naval warfare (separate ships and all) makes it hard to film. I guess one could go the Alexander the Great-route (the movie with Colin Ferrell), but that style was just terrible.
Now, the ending. I actually liked the ambiguous nature of the ending, and how Will Turner and Elizabeth Turner (married in the middle of a naval battle in probably one of the worst contrived scenes ever made) could only see each other every ten years. It was much better than the saccarine tales where everyone lived happily ever after. But Duvall has sent me to
where I discovered that that was not, in fact, the ending. I would have vastly preferred the nominally more "heart-wrenching" ending, if only because it suits my sensibilities of responsibility and adulthood better, and it's a nice way to round off the series. But of course, that closes off the possibility of Pirates 4, which, unfortunately, I'm sure someone will drag me to see.
*sigh* The series started out with such promise, but it pulled a Matrix in the end.