Our group of four enjoyed our stay at the Sif Apartments. The building looks brand new. It's situated just about a mile from most of the crowded spots of Reykjavik. We had a rental car so getting around was no problem.
The building and our rooms were overall very quiet, but there was an unexplained fire alarm one night that went on for about 10 minutes. Just as I got all the way to the entrance from my 6th-floor room, it stopped.
One thing that was tricky was the parking garage. Finding the entrance was easy, however, we had two stressful situations regarding the garage. First, it is an absolutely humongous garage that is laid out in a very confusing way. It connects to many different buildings including offices and restaurants, so it's very challenging to navigate yourself to the Sif Apt building. Plus, you have to actually enter the building from the outside main entrance since the front door code does not work on the doors in the garage. On top of that, you have to then remember the maze to find your car when you want to go somewhere. You might want to give yourself at least an extra 5 minutes to find it...no joke. Second, make sure you know how you're going to pay. You can do it via the Parka app or at one of the kiosks in the garage. Our first kiosk apparently wasn't working properly but it took us several tries before we realized that. Luckily, we found a different kiosk and it worked just fine. The Parka app is much more convenient and trouble-free.