I do like the Chelsea Pool at the Cosmopolitan. Overall, nice atmosphere and attentive wait staff and generally fun environment. We rented a day bed that was not pool side and it set us back $300 food and beverage minimum. I really appreciate that a place like the Cosmo does food and beverage minimums and not just a flat fee.
My major gripe- there is absolutely no shade at this pool unless you pay for it, and even still, it's not much. Our daybed had a mesh cover on it which didn't even help. The staff told us we weren't allowed to move the umbrellas, even though it says on the website you can request an umbrella with the daybed. We got absolutely fried by the sun.
I didn't think too much of it until I went to the Aria's similar tranquil-themed pool. Lots of trees and man-made shade. I wish we just spent our time there! But I know, the kids these days want the cool Cosmo hotel pool experience.
All in all, I'd return, but only if promised shade.