Location is excellent. It's right there in the thick of the action. Apartment is properly sound proofed so we had no problems with that. Only issue is the air conditioning. We visited when the heat wave hit so many a time the heat was unbearable as there was no central air conditioning in the room - only a portable one (which required an outlet but in opening the windows in the room meant losing the sound proofing) and a couple of standing fans.
All in all, a really charming apartment which really added to our Istanbul experience. Oh, and all of Julia and Tarkan's recommendations were spot on - no spoilers though, you'd need to stay with them to get them. :)