Isak's flat is amazing, and he was a great host. Thoroughly recommended.
The location is excellent -- there's a wide variety of shops, cafés and restaurants right on the doorstep. If you're not feeling like walking (although we walked to most places we visited around the city), there are underground and railway stations only a few minutes away. You can also get the ferry across from Slussen to see the Vasa or the Abba museum.
The flat itself is really comfortable, clean, stylish and well-equipped. There's a nice balcony, a kitchen with dishwasher, good-sized lounge, bathroom (with a great shower) and a comfortable bedroom. No traffic/street noise whatsoever, too, if you're a light sleeper.
Isak was a really helpful and friendly host. He kept in touch before the visit and was understanding when we were a little late meeting him.
Overall, we had a great time in Stockholm, and would absolutely recommend this great apartment to anyone. Thanks!