Like others, I really like this hotel. The hard product is very high quality (though not quite as colourful as on the website) and service is good, if not great. As a Platinum I was upgraded to what was either a large Junior Suite or a small Bristol Suite (apparently the only difference is size) which was well designed and furnished. As others have mentioned, the bed was comfortable and the room was especially quiet - Both of which I really appreciated as my weekday nights are in a loud Doubletree with terrible beds.
I liked the ability to eat and drink outside during the summer and I also liked that there was both modern and classical art throughout the hotel.
Sometimes the service felt like a true luxury hotel (e.g. setting up room service on a table), sometimes less so (e.g. doorman has a habit of ignoring customers entering). Overall though, this is one of the best Starwood hotels in Central Europe and I will probably stay here again on my next visit to Warsaw.