We had a really nice stay in the center of Gamla Stan. We are a family of five, there was sufficient place to sleep. The apartment was clean, modern and had the furnishings we expected.
Since this is in the middle of the very touristy old town in Stockholm you should be aware that it there is a ton of street noise and if you keep the windows open you hear it of course.
If you go into it knowing this, it can be a real fun experience for a few days.
Check in with the door codes was really easy, the host communicated reliably and promptly.
Recommended.