If will say that the Adult Only area on Oasis kicks DCL's butt so if they went alone as just adults I would expect that they spent a lot of time there. It may be one area that they don't find better but only time will tell.
I did not find our beds to be bad at all, I didn't find the food to be lacking compared to DCL and I didn't find that the staff was unfriendly in the least. Loved the aquatic show (Oasis of Dreams) but I love Cirque shows. Loved Come Fly With Me, it was amazing and also loved their ice show even though I didn't think I would. Never attempted Cats as I read tons of bad reviews. Didn't love Labadee but don't love CC either, we just walk around a bit then go back on board. Last few times with DCL we never even bothered to get off the ship. We did see lots of little people doing the wall climbing, there were some very wee ones putting adults to shame although its another thing we didn't try. Enjoyed watching others do it.
Oasis also has this dessert buffet thing on the last sea day on the boardwalk. They have different stations with cupcakes and candy/caramel apples, cakes, petite fours, I think (not sure) that there was also a chocolate fountain. They had games set up for the children and it was a carnival atmosphere. Its a nice afternoon.
If costs were the same I think I would still do DCL one cruise and then one off to RCCL. We would not strictly go back to DCL. We have the Symphony booked for our next cruise as a B2B and it looks great. There will be a puzzle room and a laser tag room. They have a few restaurants I'm wanting to try, like Wonderland and Jamie's Italian.
I love DCL but I have to give it to RCCL for some of their things.
JMO
