Concierge.com's insider take:

This 161-room hotel—composed of Baroque, neo-Renaissance, neoclassical, and modern buildings—sits on the Vltava, practically on top of Charles Bridge. Eight room grades and five suite types render it impossible to describe a typical room, especially when they land in different buildings; suffice to say that the smallest are a very respectable 350 square feet, and all have king-size beds and big tubs in the marble bathrooms. If you economize with a "Superior" (the second cheapest), book one on the seventh floor for vaulted ceilings and south-facing windows. The decor throughout is standard Four Seasons: deluxe and undemanding, in muted beige and green hues, though a recent redesign has brought a palette of vibrant blues and cool slate to the remodeled Renaissance wing; other buildings are set for renovation through 2009. Service is the thing here, and it's as impeccable as ever. There's a small gym with a sauna, a microspa (you can get in-room massages, too), and the Michelin-starred pan-Italian Allegro restaurant—one of the best this side of the Alps—which has a riverside terrace with absolutely incomparable views of Prague Castle. Favored by travelers seeking an international standard, the Four Seasons was good enough for a recent stay by Madonna, who probably recognized the advantages of having one foot on Charles Bridge: easy access to both Mala Strana and Old Town, as well as a surprisingly quiet riverbank park between the hotel and Manes Bridge, just to the north.