I'm giving this movie three stars, but I think it's the kind of film that could improve upon repeated viewings. It has a pretty good start and a good action-filled ending, but as with the second installment, the middle section leaves some to be desired.
The opening section, where our heroes join together with the once-late Captain Barbossa to rescue Jack Sparrow from Davy Jones' Locker. This involves a trip through some Gilliamesque environments (that's Gilliam-lite-esque, by the way). Particularly amusing is Jack's personal hell - a ship full of himself as crew members (this multiple-Jack effect would be used a few times later on as well, to not as good an effect as it is at the start, though). And the solution of how to escape from the underworld back into reality was particularly well-executed.
Unfortunately, once back in the real world, things bog down as the negotiations dragged on into the night. Well, not really, but this section is mostly involved with various characters acting on hidden agendas, setting up and breaking alliances, and so on. It's not particularly clear in this section who is setting up whom, and how many of our heroes are aware of the others' plans. The movie itself gives us mixed messages, sometimes dropping hints that everything is part of a master plan, sometimes not. The scene in the Bretheren Court was well-done (and smartly played by Jack), but a lot of the rest of this segment probably could have been trimmed up without adversely affecting things.
I also wasn't happy about the changes in a couple of characters during this part. The second film looked like it was going to do some interesting things with Norrington, but most of that was thrown out in this film - he gets a change-of-heart once he sees what he has signed on for, and then is suddenly (but heroically) killed off. And Davy Jones spent much of the movie as an unwilling hired gun, which had the effect of making him a lot less threatening. It's not until the end of the film when we get a little look inside his characters and the shackles come off that he regains the menace he showed in the prior movie.
And speaking of the end of the film, here's where things shift into overdrive, finally getting us out of the doldrums of the middle section. The movie sets up a battle between the pirate fleet and the East India armada, but as it ends up, there's only a battle between the Black Pearl, the Flying Dutchman and the East Indian Endeavor (why everyone else packs up and leaves after that, I'm not sure - the "bad guys" still have vast numerical superiority, don't they?). The main battle takes place in a giant maelstrom and is one of the few times this kind of sea battle was shown in an interesting and exciting way on screen (to me, anyway). Yeah, there's a few too many Spider-Man moments (Jack swinging his way just about anywhere he needs to be), and the marriage in the middle of a fight scene was a little too cute, but the action keeps moving at a fast clip to keep minor issues at bay.
Thinking back, it might be possible to work through all of the machinations of the middle section of the film, and that might bump things up to four stars. But for now, a solid three stars, and a good ending to a good series.