My spouse and I stayed here in early October on a road trip around the South Coast. I'm late with the review but wanted to make sure that I wrote one since we very much enjoyed our stay at Lambastadir Guesthouse!
The room was spacious (compared to some of our other accommodations in Iceland in the same price range) and was clean and comfortable. The beds were especially comfortable. The staff was welcoming, friendly and helpful.
The quiet, rural location made for a restful stay and we experienced a great Northern Lights display on the night that we stayed! We made use of the hot tub on site and it was lovely at sunrise.
We enjoyed dinner out at Krisp in nearby Selfoss. The town is also a convenient location to stock up on essentials if you're travelling (food, gas, etc.).
We would definitely recommend Lambastadir and hope that one day we have the good fortune to return.