We used Coliseum Hotel as a base to explore Istanbul. Location is it's best feature: in less than 5min you are in the Blue Mosque and in just 10min you can find lots of good restaurants. Besides that, the street is very quiet and good to rest. The hotel is also recent and clean. The terrace offers good views. The owner, Mehmet, is very nice and available to help you with everything.
However, as every hotel in Sultanahmet, it is a bit over priced considering what it offers. Rooms are a bit small but enough. A couple of things to improve: there are too many things in the corridors (e.g. boxes) and breakfast doesn't have fresh bread neither fruit.