I went in October 2 years ago and loved it.We stayed for 4 days and hired a car and drove the golden circle route, hung out in Reykjavik and were generally tourists! I know people slate it but I recommend he blue lagoon. Went straight after the flight in and relaxed in the hot water while it was 1deg outside with bright blue sky. That was awesome.
I recommend the lobster pot (or something) on the dock. It had a great a range of fish kebabs, soup and free coffee! Also there is a happy hour app you can download to get all the various happy hours throughout the city, otherwise drinking is not cheap!
I want to go back and explore a bit more as the people and the place was fantastic!