We have only sailed with Costa before so I can only compare these two lines. Embarking was pretty painless but you are not given the warm and cozy feelings from customer service. The ship is beautiful and big. It took me almost the entire cruise to figure out where everything was (I still don't think I saw everything). We had 2 rooms (a balcony for us and an inside stateroom for the kids). Here are some pros and cons:
The good and bad:
-Nice rooms (especially the inside stateroom-it was larger than on the Costa Pacifica).
-Good food-especially in the dining rooms. The food quality and portion sizes were better on the Fantasia than the Pacifica. I think food is very subjective though. Others we knew on this cruise didn't care for the food very much.
-Most of the shows were good and there was always something going on in one of the bars.
-The kids club was OK. My daughter like the one on the Costa Pacifica much better. Our cruise with Costa was only 2/3 full and had very few children on board. This time our cruise coincided with a European school holiday and it was completely full with a ton of kids. I think the crew was overwelmed by all of the kids.
-The room service as a whole wasn't very good. I never saw my room attendant (he never gave us ice or restocked the mini bar). He did the minimum-clean towels and made the bed. Our room attendant on Costa would wait outside the rooms after dinner to see if there was anything else you needed for the evening.
-Dinner service was pretty good. We got off to a bad start when the waitress gave us a bottle of wine that was not on our wine package (b/c they had not delivered the coupon book to us yet). It was a cheaper bottle of wine than we had in our coupons but they still made us pay for it because we didn't have a coupon for it. We told them to take one of our coupons for it (the bottle they gave us was 1/2 the price of the bottles in our coupon book)but she couldn't. I guess they don't trust the wait staff and keep a tight record of the wine bottles. Those coupon books are retarded-why can't they just upload everything to your card? It was uphill from there and we received pretty good service. The dinner service on Costa was much better though-our drinks were poured and ready for us every night and several bottles of wine were waiting for us to try and choose from. I think the full ship had the waitstaff overwhelmed on Fantasia. On Costa we had much better service I'm sure due in part to the ship not being full.
-I would suggest eating in the dining rooms most of the time. Unless you hit the buffet for a late lunch it was really busy (the breakfast was crazy most of the time too). The dining rooms never seemed too busy.
-We do our own excursions-the shuttle buses and excursions are too expensive on these boats (especially for 5).
-Disembarking was chaotic for those who needed to retrieve their passports.
My advice to Americans is to go ahead and try MSC. You might want to do it with one of those last minute discount fares. See if it is for you. Try to go when the schools are not on holiday. We really did have fun and I loved sitting out on the balcony and relaxing while looking at the beautiful French Riviera. We live in Europe now so I know about the customer service (or lack of)and was prepared for it. I have never cruised on an American line though. I was told the American lines spoil you. MSC was fun though, and I thought a really good value.