I've never been to Port's o call except for the lobster festival that takes place there in mid september so I can't really say what it's like there on a normal day but Lobster Fest rocks. You get to see cool bands because they do it with indie 103.1 and the lobster is cheap but is still good lobster. It's less than 20 bucks for a whole lobster. They also have a dog costume parade which is not my thing but I can see that some people would like it.
Pros: Lobster Festival
Cons: Not much to do there if its not lobster festival time.