I was the only person, so it was essentially a private tour. The guide was wonderful. He was friendly and very knowledgeable. He gave me enough time to walk around each place on my own. We had a nice lunch inside the Topkapi Palace, and I got addicted to apple tea.
The only part of the tour I didn't care for was the visit to the rug gallery. Since I was the only person, they had a captive audience. Though I did see many beautiful carpets, I didn't know enough to actually invest in one. I had to resist giving into the sales pitch. What I was more interested in were the ceramic tiles and brilliant plates they had.
Most of the sites are close to each other, so you'll walk most of the time. I didn't mind it because everything was so interesting. It was almost a visual overload. Just remember a lot of these places do not allow flash photography, so bring a camera that can take good photos at slow speed. Also, no photos allowed at all of the artifacts inside the Topaki Palace.
The visit to the Grand Bazaar was mainly just a walk-through at the end of the tour. My hotel was only a block away so I went back in the evening and bought some souvenirs.
There's much to see in the old part of Istanbul, and the tour covers the most essential places. Many guidebooks recommend a few other places like the archeological museum and Suleymaniye mosque, which one can explorer on his or her own.