I think it is impossible. I read many comments that say things like "you'll love the ship" "food and service are great". I think that's misleading. If you know specifically who is serving someone you can predict this. Otherwise you can't. You can go on any specific ship and get great dining room service while somebody else on that same ship had horrible service. This is true of any ship of any line. Food can change as well from itinerary, to provisioning, to executive chef, to individual supervisors in the gallies, there's just too many variables to say because it was good on a cruise in June that it will be good on the same ship on a cruise in November.
The service can vary. Crews don't stay on the same ships. They move around. A master/Captain can make a big difference in the attitude of the crew as in easy going to more tense and less interactive.
The only thing that stays fairly steady is the physical ship. And, just because you find it nice, others may have different opinions. So, I think something more descriptive, size, amount of balcony cabins, size of cabins and categories, amenities, etc. rather than subjective (beautiful, stunning, lovely), is more helpful.
If someone is going on the Galaxy, a ship I had a magnificent experience on, and others have had recent miserable experiences on, I can only tell them about the ship and wish they had the experience I had. But even still, they may like totally different things than I like, and may not have thought that my Galaxy cruise was as magnificent as I did.
You are so right, it totally amazes me when I hear 2 very different reviews of the same cruise. Seems you hear a lot about food, now everyone has different tastes when it comes to food, for me its easy, I don't go for the exotic dishes, just plain and simple, but if its supposed to be cold, then it should be, same for hot..
I think service is also questionable, you can have a wonderful waiter, while someone else may have a new hire who is just learning the ropes or has too many tables to adequately service them all 100%. So, yes you will find different expierences on the same cruise, just a way of life I think?
I already know and expect I will very much enjoy our next cruise on Radiance, in the past have been very pleased with RCCL and their ships, so the only way I will come home disappointed is if there is really something wrong, including bad weather, that can really dappen a cruise.