The port is just average. You get in to port at 8am, but none of the shops or anything actually open until 10am. My suggestion in this port would be to head straight to the beach. Avoid the straw market, there's nothing that great there.
This port was nice, there was some good shopping, but it was extremely crowded. When you initially get off the ship, keep an eye out for the Iguanas! They are very social! They like to hang out on the rocky area in the port by the water. They were very happy to come right up to you and lick your hand. The bad thing about this port is catching a cab to the downtown area. The lines are long, they practically pile you on top of each other and then, halfway through your trip, they pull over and collect the money. They should have just collected it when you got on if they were going to do that.
I had a fantastic time in St. Maarten. There were lots of great little shops, beautiful beaches and a lot of great little bars. For around $7 a person you can buy an all day pass for the ferry from the port to the downtown area, which makes it easy. There is a lot of great shopping and not nearly as crowded as St. Thomas. All in all, it was a great time.