We went for four days in January, really enjoyed it. Did golden circle, northern lights trip and blue lagoon, all very good.
Get yourself to Hereford steakhouse in Reykjavik, fillet steak was fantastic as where the banana split. They also do puffin and whale if your feeling adventurous.
Local beer Gull is a good drop.
Take plenty of money though it’s not cheap over there. And whatever you do don’t disrespect the “hidden people”