Just returned from a five night stay at the Prague Marriott and can recommend it highly!
From the first hello upon checkin to the last "goodbye - come back soon" it was terrific. The location cannot be beat, it is walking distance to nearly all the major sights and easy transportation.
The Concierge Lounge served more than adequate breakfasts, snacks, cocktails and late night desserts. It would have easily been enough to have all your meals there, but too many good restaurants abound in Prague!
The concierge staff was most helpful planning day trips, concert tickets, arranging car service, airport pickups etc. Five star service all around!!!