Our room #405 overlooked the Harpa Concert Hall (beautiful modern glass building with the harbor and the mountains behind it), the Culture House, a city park, was right next to Bus Stop #6 for Flybus (airport shuttle) and tour/ excursion pick-up's, and was within a 10-15 minute walk to many attractions, restaurants and shopping. Location amazing! No special perks as others have mentioned even though part of the Marriott system. Was not extraordinarily expensive given that many hotels are very very expensive in Reykjavik.
Pros: Lobby and bar beautiful. Staff courteous, friendly and efficient. Very clean, comfortable beds. Liked the modern aesthetic of the room. Lots of light through the windows, but with well fitted black out shades (not needed as much for us given December). Great desk with multiple outlets overlooking the view. We went to a bar across the street for dinner, Islenski Barinn - reasonably priced, very lively (long line out the door, though we got there at a lucky moment and got right in), very friendly and welcoming, and the food was terrific!
Cons: No outlets next to either side of the bed, really unacceptable! No teapot or coffee pot, major bummer in the mornings. Halls are very dimly lit. The bathroom and bedroom are wide open to each other, that's not so appealing, though the glass enclosure around the toilet was fine. A bit more storage/ bigger closet would have been appreciated.
We were there off season so the hotel was sparsely occupied and no loud noise from neighboring restaurants/ bars, but I could see this as a potential problem during holidays/ in high season.