I've cruised on QM2 and was not at all impressed by either the food or the lackluster service. We had two QG suites and were greatly disappointed in the menu for the QG. We were amazed and disappointed that the menu in the QG was exactly the same as in the main dining room. Yes, you do have the ala carte menu, but that never changes and you don't want to eat the same food off that menu every night. For the money, and if you really want to cruise Cunard, save the bucks and stick to a non Grill class cabin.
I've been on 45 cruises, on just about every line out there, and for me, it's either Seabourn or Crystal. Since you're asking about Crystal, I'll keep my comments to that line. Their ships are much smaller than Cunard and so you get personalized service. The word "no" isn't in their dictionary. Crystal has ranked at the top of all the national travel magazines since they started. Their food is excellent and they have two alternate dining rooms that serve some of the best food at sea. Crystal also has the best in terms of daytime and evening entertainment. Their Creative Learning Institute is something no other cruise line has with their classes in foreign language, art, music, investments, health and wellness, computers and photography and food and wine. They bring in world renowned guest lecturers for each cruise. Their shore excursions aren't cattle calls and they keep the number of participants at a much lower number than any other cruise line.
Crystal is a very formal experience. On a typical 12 night cruise they will have three formal nights, three or four informal nights and the rest country club casual. Unlike what I experienced on Cunard, Crystal passengers don't go back to their cabin and change into shorts and t-shirts after dinner----they remain in the dress code of the evening for the entire evening.
Soft drinks, specialty coffees and bottled water are included in your cruise cost, unlike Cunard that charges for those things.