This is my top pick for a Mexican cruise - Carnival Spirit is an excellent ship - smaller than average for Carnival but still new. Less crowded but the same great Carnival fun & food.
The itinerary is the best - Acapulco is a very interesting city. Personally, I like to take a taxi out to the Princess Hotel on the beach outside the bay. The swimming is excellent and the grounds are beautiful. It is where Howard Hughes was living when he died. There are beautiful pools with swim-up bars, peacocks, restaurants... and the beach has bathwater but with big waves like you see in san Diego - Pacific waves, not Caribbean ripples.
This ship/itinerary was three times the cost a few years ago.