I understand you had some disappointment with the food and you are, of course, entitled to your opinion, but I thought I would throw in my 2 cents as a seasoned cruiser. I've been on 7 Carnival Cruises, including the Glory in 2004, and about to leave on the Glory again this Saturday. Never has my food been luke warm.
Tip: when eating from a buffet, first walk around the buffet and look at what is offered and make some decisions about what you would like before even taking a plate. Next, make your cold food selections, i.e. salad bar, fruit, etc and take them to your table and eat them. After that, return to the buffet and serve yourself the hot foods that looked good to you when you scanned the buffet offerings earlier. Walking around with hot food on your plate trying to decide what to eat, OR leaving hot food on the table while eating your salad will surely result in luke warm or even cold food.
If you happen to have the experience of dining room food being cold -- send it back.