Perhaps others can comment about the Cosmo pools - we've stayed there but did not use them. At the Cosmopolitan there are some negatives regarding such things as service and room location which I'd encourage you to research thoroughly (here, Tripadvisor, etc.) however it is a very nice hotel. If I were to sum up it's shortcomings I'd say since it's not a Marriott it lacks the "friendlier" service one usually experiences. There is no status recognition of any kind and food in all their restaurants is quite expensive by any standard - especially Las Vegas. For example, our last time there our room included breakfast - a credit of $60, and the breakfast-serving restaurant was closed for some reason leaving room service as the only option. A very basic breakfast exceeded the credit by quite a bit. It was good but not an experience I would want to repeat every day. Ask for a room with a balcony overlooking the Bellagio fountains... you won't be disappointed.