If you're looking for a nice hotel downtown, this is a great place to stay. The JW Marriott is perfect for someone just looking for a nice bed and little more. There is a pool but it's nothing special.
The decor and style of the hotel interior/rooms is a little outdated. There are so many great boutique and modern hotels throughout downtown Miami (even the JW Marriott Marquis) that are the same star rating but much nicer. This hotel does not have floor to ceiling windows like many others downtown and very few rooms have a water view.
I have no real complaints as the staff was friendly and welcoming -- but in this price and star range I just didn't feel that it was as nice as it could have been.