Sequels are a tricky business. It's so hard to live up to the first one, let alone surpass it. More often than not, sequels often just feel like vain imitations/remakes/rehashes of the films that spawned them as the same basic formula is usually just flogged to death (Rocky's 2-5 and Matrix's Reloaded/Revolution come to mind here). There are exceptions, such as "The Empire Strikes Back", but they are few and far between. For the most part I enjoyed "Dead Man's Chest" but I cannot deny that the original film was superior.
The biggest sin of "Dead Man's Chest" is that it runs too long and tries to over-stuff itself, cutting back & forth between Jack Sparrow's antics, the misfortunes of Will or the misfortunes of Elizabeth, which then leads us to the misfortunes of Norrington, with a lot of action thrown in, whereas the first film had a more focused, driven feel to it. I saw the film with my dad and he commented that it felt like they took a book, ripped out the most interesting/exciting parts and then pasted it together in no particular order. Most criminally, the storyline with Will catching up with the sea zombie version of his father Bootstrap Bill Turner (Stellan Skarsgard buried under tons of prosthetic makeup & CGI) is probably the most interesting storyline going in the movie, but it deserves more time than it ultimately gets. The decision to turn Norrington into a full blown evil bastard was unexpected - I know he wasn't exactly the hero of the first film, but he wasn't the villain either, just the romantic rival (I blame this on the fact that they cut scenes that were meant to establish him as a nicer guy). The thing with Elizabeth becoming infatuated with Jack, or at least appearing to become infatuated with him, was a relatively minor offense but still an annoying one. It felt like the writers were trying too hard to both play to the popularity of Depp/Jack and also to try and resurrect the opposites attract magic of Princess Leia & Han Solo, the primary difference being that Solo was taller, better looking, had better equipment and had better hygiene than Sparrow. That seemed to go against part of Elizabeth's realizations in the first film that pirates weren't all they were cracked up to be, and she struck me as being smarter than to fall for an obvious scoundrel like Jack. Or maybe I'm just over-reacting to their decision to put the young lovebirds fate in doubt. And there are some who will undoubtedly be annoyed by the cliff-hanger setting up "Pirates 3: The Pirate Version of the Search For Spock".
Okay, stuff I actually did like... there were some genuinely funny moments (some of which were overplayed), the action set pieces were well staged & well executed (if a little over the top), and the actors were generally good. Johnny Depp basically rehashes his performance from the first film, which works well enough since he still appears to be having fun as the drunken glam rocker pirate. Orlando Bloom is good in his usual low-key way (though he's basically got himself typecast as the earnest young hero and will probably spend the rest of his career being accused of just playing himself in every film he does).Nighy & Starsgard were good along with the rest of the undead crew, though they are basically a steroid fueled remake of the undead crew from "Curse". Keira Knightley was alright, though in a few scenes it felt like she was trying too hard (namely the ones where she's supposed to act like she's becoming infatuated with Jack). I guess I'm not being very positive here, am I? Well, if I make the film out to be worse than it actually is, I'm sorry. Just go in knowing that it's not as bad as the Star Wars prequel trilogy, Batman & Robin, Daredevil, Elektra, 2005 Fantastic Four and Catwoman.