When asked what about these movies that make me never get tired of them, I can't find the specific answer XD 

But, I guess mainly because I like the characters' transitions in becoming friends-foes. And by that I mean how all the characters, who are practically criminals, fight each other to achieve their own goals, but then at some point befriends each other, then fight again, then together again, back and forth like that throughout the whole series.  But in the end, everybody's happy except for the true antagonists (like Lord Beckett and Davy Jones in the 3rd movie).