Not much to do there unless you want to fish or take a water taxi. Your arrival is like walking into a flea market. It is super packed. The day we were there four cruise ships pulled up with us. They have to use tenders to take you to the port which is time consuming. HUGE amounts of college kids on the beaches.
DO NOT book with carnival as it is way more expensive. If you book directly with vallarta adventures it is $90 for the extreme tour. The only difference is you avoid the chaos at the port trying to get on shuttles and you take your own taxi to there office where everyone from the ship is heading . It is approx $2 per person and less than 5 minutes away. From the office you are taken on your excursion with the cruise people. When the excursion ends, if you booked with Carnival, they take you back to the boat, if you booked direct they take you back to the office. Since we were the only two people directly booked, they took us back to boat with the rest of the cruisers which was great.