I feel I should give a caveat. I love movies about pirates. I love movies that have big sailing ships. I own all of the Pirates movies and even own the Geena Davis pirate movie Cutthroat Island. One of my guilty pleasures is the movie Captain Ron, not because of the story but because it features a beautiful ship. I'm not sure where this love of Pirates and sailing ships comes from. I grew up in a completely landlocked town and even though we went to the beach a lot on vacations, I don't think I've ever been sailing. So why I respond so strongly to the notion of sailing a ship and being a pirate I'll never know.
I only bring this up to show that I am biased. If you make a movie and put in some swashbuckling adventures, a nice ship, and/or a healthy dose of fantasy magic and I'm going to like it.
As for On Stranger Tides, I really liked the movie. I loved the costumes and the sets, including the ships that they showed. I enjoyed the characters. I liked that they added a bunch of new characters instead of relying on the same old ones. It was definitely time for some new blood. I really enjoyed the character of Blackbeard, who was just a great villain. I really enjoyed the special treasure he kept in his cabin. The story was action packed and had a good pace. For the most part I found it easy to follow along with, though there were a couple of elements I didn't quite get. I thought they had an interesting take on the mermaids, but I would have liked to see some mermen too. Overall, I thought it was a good film.
It is getting some pretty poor reviews unfortunately. I think people for the most part feel a fourth movie was unnecessary and weren't really willing to go along with the adventure. If you like pirates movies and are willing to go along for the ride I think you'll enjoy the film. If you go into it with a negative attitude and aren't willing to go along with it, you will not be satisfied.