We had some time before we embarked on our cruise round Iceland and this garden was within walking distance of our hotel (but not near the centre of Reykjavik).
It was better and much more interesting than I was led to believe. We had a good conversation with one of the friendly gardeners who was obviously passionate about his work.
The garden is laid out like a park, with a stream, colour co-ordinated borders, and amazing rockeries. There are also more formal beds with plants organised by family.
The cafe in the centre looked good but we did not try it.
Having been brought up in Oxford, with its world famous and ancient botanic garden, I would say this is not in the same class, but you will be amazed at what can be persuaded to grow in these climes.
Definitely worth visiting if you have an hour or two to spare.