The pier in Progresso is over 3 miles long. It boasts to be the longest peir in the world. When you get off the ship you take a bus to the town. You are not allowed to walk (not many people would want to) because the peir road is still under construction and it is not safe.
When you get to the town it is a little village on a great public beach. The village faces the beach and you can walk over there at any point as you walk through town. It is a large beach and a small town so I wouldn't expect it to be too busy in the summer. (We went in February)
The pier is almost 5 miles long. We were also there in Feb and it was empty. My understanding is, Progresso's a vacation spot for the nationals. The town's population was 30K when we were there but swells to over 200K during the season. Water is not as claer as Cozumel but beach is nice. There's pictures in an album titled "Glory 2,28,2004".
I was in Progreso 2 weeks ago and we went to the beach. DEFINATELY do not pay for a beach excursion there. The free shuttle buses will take you from the pier to the town square where you will be dropped off in the small shopping market and the beaches are only a 2 block walk from there. The beaches are very nice. Beautiful white sand , although the waters are not as blue and clear as Cozumel( this is still the Gulf Of Mexico) they are still very nice and warm. There are great little restaurants to eat at and the waiters will bring you drinks out onto the beach wherever you make your spot. The people are very friendly and very accommodating. Enjoy!