Kos is a fantastic little island, just a three-hour flight from Brussels.
The TUI BLUE Palazzo del Mare hotel was excellent. If you have a room by the large pool, you have your own ladder to step directly into the water. The staff were incredibly friendly; I had a kitesurfing accident, and the hotel responded very quickly by sending a doctor and then taking me to get X-rays. The adults-only policy makes for a very peaceful atmosphere. There are a lot of German guests, but they don't cause any disturbance.
The kitesurfing spot isn't ideal, as the wind is predominantly onshore, which can make riding tricky. Fun2Fun is the only kitesurfing club nearby, and they have good rental gear available if needed. We were lucky with the wind, but there was absolutely no wind the week after our visit.
Kos Town is well worth a visit, with plenty of shops and restaurants.