Concierge.com's insider take:

Istanbul is fast becoming Europe's capital of cool, and its hip-o-meter certainly clocked up a couple more notches with the April 2008 opening of the W in the unlikely (but still central) neighborhood of Beşiktaş. Set in a perfectly preserved four-story 19th-century residence that once housed officers from the nearby Dolmabahçe Palace, the hotel's interior is every bit as modish as its global counterparts, with an extra layer of Ottoman opulence worked in by Istanbul's designer du jour, Mahmut Anlar. Rich black-and-white fabric patterns adorn the upholstery in the purple-tinted downstairs lounge, Sip, while the main bar in the first-floor "Living Room" is crisscrossed with traditional latticework set against the W's signature deep-maroon tones (it's a great spot for pre-dinner cocktails, even if you're not staying here). The restaurant, a branch of Jean-Georges Vongerichten's Spice Market, from New York City, is excellent. The smaller standard rooms are ample and cleverly laid out, with bathroom sinks embedded behind cupboards to save on space; try for one on the ground floor for a little private garden, or on the second floor for a funky wooden cabana connected to the room via a walkway. What the W lacks, alas, that other hotels in Istanbul can boast by the bucketful, is the uninterrupted Bosphorus panorama; however, for a view of the newly developed upscale shopping street outside—part of the same development—go for one of the brighter and more spacious "Fantastic" suites.