I just returned yesterday from the Elation which had the same itinerary as you: Grand Turk, HMC, and Nassau.
This was my 19th cruise and I live in Florida and I don't usually enjoy water that is under 80 degrees, so I did not do any excursions that involved water, but some of our tablemates did.
My parents will be on this same cruise in March and here is what I am telling them.
Grand Turk is a very new port and very undeveloped. The Cruise line dumped a TON of money into building the pier and the shops connected thereto. Other than the handful of shops right at the pier, there is NOTHING worth buying in local shops. This is not a shopping destination. There is really only one jewelry store there (Goodmans or Goodmarks..my wife would know the name, and it strangely had two separate stores). Most of the other stuff is typical island stuff (Del Sol) and island trinkets.
I stronglky suggest that you book an excursion while in grand turk or don't even bother getting off the ship unless you just want to visit the beach adjacent to the pier.
I always book my own excursions (a lot cheaper than what is offered by the cruiseline) but my reasearch indicated that the only one worth doing on my own would be to book a local dive operator to take me to the 7000 foot drop off. I didn't feel like getting in the water, so I booked the dune buggy excursion through Carnival.com which was good because there was only room for 4 couples and the excursion sold out before we even boarded the ship. Again, in Grand Turk, you need to probably pay for an excursion or just lay on the beach right next to the pier. There is a nice Margeritaville adjacent to the pier that has a big freshwater pool. The music is loud (they had a dj) and they appear to want to be like Carlos and Charlies or Senor Frogs.
Both of our tablemates (a total of 8 people) did the Gibbs Cay snorkel with Stingrays and they loved it.
As for HMC, the only thing to do there is relax and do water sports. They tell you onboard that there is zero shade and you must rent a clam for shade for $15. While you can find some shade beneath some of the australian pines, I suggest spending $15 for a clab. Basically it is a blue canvas thing that you pull over the top of two lounge chairs and it provide shade for 2 people. I got on the beach at 10 am and had no problem getting one, but I heard that by noon they were sold out. You can also rent a cabana which is a wooden structure that can accommodate an entire group (some groups had 15 people partying there) and it even has air conditioning!
The food buffet is only so/so and the lines were chaotic. I got in line at 11:45 right after they set up and had a 30 second wait, but I talked to people who lined up around 12:45 and they had a 45 minute wait.
In Nassau the weather was cool. Many people left the ship with sweaters in the morning, but a few hours after sunrise, it warmed up, but I would have been quite cold if I had been in the water.
As for the ship itself, it was okay, especially given its age and smaller size in todays world of mega ships. The crew was just average, and we encountered several crewmembers who were rude (a first for us after 19 cruises). The cruise director has a staff of young people that appear to be too inexperienced to be in their positions. This was also the first cruiseship on which I repeatedly heard the cruise staff refer to the ship as a "boat." Anyone who has cruised before knows that the Elation is a ship, and if you need to evacuate in an emergency, then you get into a boat.
The frozen yogurt machine rarely worked properly and the cheesecake was hit or miss. I ate cheese cake every time it was available and twice it was good (the first day at lunch, and the only time it was offered in the diningroom as a dessert). All of the other times it was terrible. The eggs offered on the Lido deck for breakfast ranged from average cruise eggs to terrible eggs that resembled the cheese that you get at Taco Bell when you order Nachos.
They do offer a chocolate cake thing every night for dinner that was outstanding. Also they offer Salmon as an alternate entre that was very good both times that I ate it.
Hope that helps.
Overall, it was a so-so cruise. I would not select this ship again unless it was significantly cheaper than ther other comparable options. This particular cruise it was really cheap for us (the same price we paid for the Elation's 5 day cruise would have only given us a 3 day cruise on a RCL ship).
If it is your first cruise, great. If you have been on many cruises, keep your expectations just average and you will be satisfied.
If you have been on some of the larger ships (even Carnival's larger ships such as the Glory or Pride) then you will see a marked difference on this ship. However, if you have only been on smaller Carnival ships (such as the Fantasy) then you will not see much difference from the Fantasy. Personally I liked the Eleation's decorating better than the Fantasy, mainly because the Fantasy had too much neon for me.
this is my 7th cruise and the 5th with cranival and i cant get enough.