Pirates II. Thankfully I had not told anyone else how awesome I thought it would be.
I also was severely disappointed in the Matrix sequels. The second one I hoped suffered from middle-chapter-syndrome so I managed to get good and excited for the 3rd. I should have quit while I was ahead.
You're right...the Matrix sequels suffered from being basically one long movie cut up into two parts. Had the two been meshed and cut shorter, it'd probably been a better movie. I think there was way too much side plot that it took away from the main plot and that was the assualt on Zion.
Pretty much the same thing with the Pirates sequels as well, but not quite as bad. They were a bit more self contained than the Matrix sequels. I mean Matrix 2 just kind of ended with a sudden "to be continued".