We (married couple, no kids) love the W because of the cool and stylish hotels they make. The W south beach is another cool location. Service, rooms, beach, bars, SPA, etc. is all on the levels you expect from a 5* W, but this time (23rd of March 2014) there is a huge backdraft on my otherwise spotless W reviews: the noise next door. The hotel to the north has put up extra A/C generators (or whatever these things do) and the noise is going on around the clock on a level that I have to warn fellow travellers!
I hope the W will put up some updates on their sites on this or comment on this post when the noise is gone. But we paid extra for the nicer Mega suites and we get more noise than the other parts of the hotel, because the suites are closer to the north.
Really the only downside so far, but a big one :-(