I visited Progresso on the Carnival Pride in April. I have to admit, it wasn't what we expected but we did have a good time. We had done several excursions already and this was our last stop so we just wanted to enjoy the city. It's what you make of it I guess. I would recommend either staying on the ship or doing an excursion. From talking to fellow passengers, I think the majority felt the same way. The pier is so long you have to catch a bus to shore so it is not easy to travel back and forth and there is nothing other than a few shops and a small craft market. Some passengers took advantage of the beach too.
I got the impression the ships only stop there for the few excursions that are offered. Maybe others will post their experiences so that we will know what else is out there. I'd go again depending on the rest of the itinerary.
NCL Sun, Oasis OTS, Navigator OTS, Legend, Fascination, Emerald, Glory, Mariner OTS x 2, Sovereign OTS, Celebration, Miracle x 2, Pride, Fantasy