It has the natural beauty and lots to do. Scuba diving, whale watching, blue lagoon, geysers, etc. The food is also wonderful (even the street food). The weather is also very nice as it is not too cold nor hot.
If you're into animals, you can go puffin and whale watching. If you like natural landscape there's gullfoss falls, geysirs. Also, the ridge separating the North American tectonic plate and Mid-Atlantic plate, you can go scuba diving in the waters that separate it. Iceland has great water so to speak, so a lot of people go to the swimming pools and the geothermal pool blue lagoon is a big attraction. Water is crystal clear wherever you go, so they always make good pictures. Also, food is amazing. Great seafood, and the most popular restaurant is a hot-dog stand. You can Google it and Bill Clinton has even stopped by to eat there. If you're into technology, you can tour their geothermal plant. Iceland is 99% powered by renewable energy so it's pretty neat to get to walk around their plant. There is literally tons to do in Iceland and I'm sure you'll have a great time.