Carl's apartment is spacious, comfortable, very nicely designed and well furnished. The balcony (over an internal courtyard) is lovely and secluded from the street. We loved our 2 week stay!
The Vasastan location is great. Downtown is roughly a 15 minute walk. There is a T-stop just around the corner, along with numerous bus lines. Likewise, there is a grocery store and a Systembolaget (alcohol store) close by, as well as numerous restaurants.
Carl is a straightforward and very responsive host, answering questions usually within an hour.