This movie is good pretty much for one reason: Johnny Depp as Jack Sparrow is about as entertaining a character as you're ever likely to see at the theater. Of course it helps that it was a huge production with tons of money to throw around on special effects.
Once you've seen this movie a few times, you start to notice that what at first appear to be plot holes are actually more or less covered by the script. For instance, the cursed pirates don't show up as skeletons in the first scene they're in because there are clouds in front of the moon. Jack Sparrow gets cursed but Elizabeth doesn't because you have to actually life a coin out of the box to be cursed, not just have it in your possession. Stuff like that.
But a few things remain. If Will Turner looks so much like his father, then why don't Jack and the cursed pirates recognize him? "He's the spitting image of Bootstrap, come back to haunt us!" or something similar is what one of the pirates says upon learning of his identity. Yea right.
Also, the rules governing how exactly the curse works seem to be pretty arbitrary. At one point Barbossa says that he can't feel anything, then later declares that Elizabeth's dress is "still warm." What was that, a lucky guess? And the other pirates seem to feel pain quite a lot, most notably the two "comic relief" pirates. For instance, when Elizabeth dumps the hot coals on one, and then the wooden eyeball "spliters something terrible."
Speaking of which, the wooden eyeball jokes are awful. I don't know who they're aimed at, since I can't really think of any age group or movie audience who would be amused by such tasteless jokes.
I don't think I've stressed the saving grace of this movie enough. Jack Sparrow really does rock. Where he could have ended up being a boring "Yar me matey, I want to plunder your booty" type pirate, he ends up being the best thing about this movie and makes it definitely worth watching.