I've stayed here over a half dozen times on various DC visits for business and pleasure, so these are general impressions gathered over time.
The building design provides for some odd room layouts. Generally price maps well to room quality (duh). For instance, lower priced junior suites are smaller and some are located over the main entry. These tend to be smaller, gloomy and within earshot of regular freight trains. More expensive ones face the Potomac and are a bit more spacious (2d bathroom, etc) and quieter.
Positives: Perhaps the best location in town for the Smithsonian mall. All major sites are within walking distance and there is a subway stop about 4 blocks away. Cityzen restaurant is excellent (pre-arrival reservations are a good idea).
Negatives: Breakfast quality has fallen and the restaurant now offers a very conventional buffet with no daily variety. This is a conference hotel and can be overrun with groups at times. The spa is small and can only accommodate a few guests per day. Pre-arrival reservations are essential. The lobby lounge often fills with conventioneers and can be quite loud and overflowing. Staff are hit-or-miss. That applies to upgrade availability if you book on a credit card program that offers when-available upgrades (it may, or may not, be offered at the time of registration, even if the hotel isn't full).
All things considered, I tend to prefer to stay here although it isn't quite as special as it was when the hotel first opened.