"Fun" is the word I see thrown around to describe the Pirates sequels. It's also the word I see when people try to defend the Transformers sequels as good movies.
Pirates 3 is an ungodly catastrophe, but Pirates 2 has plenty of serious problems- most notably, the plot moves nowhere. Yes, we're introduced to a couple new characters and locales, but there's little substantial development, and the end of the second movie feels like the completion of a big loop back to square one. Also, the unbelievably good writing of Pirates 1 just... disappeared in the sequels.
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http://www.youtube.com/watch?v=SBpfwpOPXNc&NR=1&feature=fvwp
~Pinkie Pie is the best pony~