The first one is excellent.
The two sequels put together and heavily edited could've made one really solid 2 1/2 hour flick, but the almost 5 hours between them was a bit much. There was one review that suggested that the writers had created an entire mythology in the first film, spawned mostly from a theme park ride, and then spent the two sequels trying to show everything they had suggested in the original film...and I kind of agree. However, Johnny Depp, as always, was excellent, even during parts when the plot was frighteningly thin. Orlando Bloom = creepy without the Legolas wig. Seriously, dude. You're creepy looking. Keira Knightley is cute, but needs a double bacon cheeseburger reeeeallly bad.
The two Pirates sequels are kind of like Yes'
Tales From Topographic Oceans...about half of it is really good stuff, and the other half is the creators kind of splooging all over themselves.

If you're at all into the cinematography/visual aspect of movies though, they're all worth seeing...obviously with the kind of budget they had, the visuals, sets, and effects are all top-notch, and far more impressive (to me) than any of the over the top CGI-drenched comic book movies. For that reason, I thought the third one was worth seeing in a theater vs. my crappy-ass TV.