From what I've read, they don't plan on doing a fourth movie for some time. I was generally quite satisfied with the third movie and thought the last hour or so was some of the most captivating stuff I've watched as of recent. In comparison to it's previous two, I'd rate it higher than the second which I wasn't particuarly impressed with but still nothing compared to the original.
I've always though that the first movie was definetely the best and really captured the pirate life and entertaining sea/sword battles. Whereas it kinda got more drained and farfetched as the trilogy continued. The story was also far more simple in the beginning, at stages in 2 & 3 I actually found myself lost within the plot.
Overall it's a fantastic trilogy and unmatched in the genre atm

, look forward to a fourth sometime in the future although it may do more harm than good.