It is very hard to compare the two as they are very different.
The Poly theme is that of a secluded, self contained beach resort in Polynesia. It is very tropical, with lush walks that lead all around the resort, a nice sand beach (no swimming in the lake), a volcano pool, dark wood and decorations, lots of tiki torches and the like. Someone who has stayed there can elaborate. We have just walked around. There are nice full service restaurants that go along with the theme and decor.
The CBR is light and festive. You have Old Port Royale which serves as a bustling Carribean marketplace. Lots of colors, sounds and activity. The various 'countries' are spread out around the resort, each one a diferent pastel color - much like you will find in many of the islands of the Caribbean. The themeing of the 'countries' is somewhat limited, but the walks, paths, and pools are all nice. Now that I reread your post I guess you know all that.
One is immersion in a quite polynesian resort, one is a taste of the bustle and activity of the Caribbean islands. Very different.
Hope that helps.
