We spent our first 6 days in Istanbul and visited most major and minor tourist attractions. In line with our experience in Ireland, we found Rick Steve's guide superior to the other guidebooks for pointing out the more interesting sights, as well as being up to date and generally interesting to read. The weather in Istanbul was pretty bad when we were there and our umbrellas were frequently used. Our last day in Turkey was also spent in Istanbul and that was our only sunny day in Istanbul.
We are normally frugal travellers, but this time we "splurged" and stayed in Hotel Sultan Hill. It was well worth the extra expense because it was well maintained, the staff was very helpful and friendly, our room had a great view of the Blue Mosque, and the breakfast was ample. Because it was cold, and also because we are not party people, we stayed indoors every night except for the first when we went around taking night photos.
We particularly enjoyed visiting the Hagia Sophia (amazing what the Byzantiums managed to build in the 6th Century), the Rustem Pasa Mosque (a small intimate mosque with fabulous Iznik tiles), walking across and under the Galata Bridge to watch the fishermen, and the Kariye Muzesi (Chora Church Museum - great mosiacs). Our Bosphorus cruise day was literally a washout, and at the end of the cruise in Anadolu Kavagi (Asia), we were overwhelmed by the restaurant touts competing for the scant number of tourists in low season. As expected, I did not enjoy the shopping experiences in the Grand Bazaar or the Spice Market because of the touts and the crowds, but Serene enjoyed walking around the Spice Market. We sampled ample amounts of Turkish food, drank lots of Turkish tea (we tried and did not like Turkish coffee), and Serene really enjoyed the sweets from Ali Muhhidin Haci Bekir, which has been in business since 1777 and supposedly invented Turkish Delight.