Stayed here with a group of friends for 3 nights- we had 5 rooms in total. Only one of our party was semi-satisfied with his room, the rest of us weren't. The hotel is very loud- street noise, air-conditioner noise and especially the bar on the roof which was open till at least 3am!
There were many other problems besides the noise- hot water not working, heating not working, towels not replenished, poor cleaning etc.
The staff were nice enough and did tend to the problems after we alerted them, but it seemed to be an endless list of things needing doing.
The breakfast was ok (although the coffee and juice were awful) with stunning views over the Bosporus- nice selection of cheese, olives, bread, yoghurt with honey etc. Although we would have liked some fruit.
As others have said, the location is very good- there is also a nice cafe next door and bars, clubs and shopping nearby. It's also only a short walk to the various tram lines when you get bored of the constant strain of dealing with Istanbul taxi drivers and their money-making ruses.
