Haven't cruised MSC Opera myself, but as I have seen, it looks like a very great ship. Really!
If you want to take a look inside the public rooms and the different staterooms onboard, there is a great "Virtual Tour"-function and a lot of picture at their website, www.msccruises.com
As I can read at their website, they're supporting a lot of diets. Just tell them when purchasing your cruise vacation.