The island is beautiful and pleasantly unspoiled, given that it is just 2 hours away from Athens. It is actually one of the least exploited locations I have seen in Greece and yet one of the best places, with a whole lot of perfect uncrowded beaches, crystal clear water (Kalamitsi, Zorkos, Vitali, Peza, and many others. Difficult to find a bad one.), nice villages (Batsi) and restaurants (Very good and not expensive, as common in Greece). Quite uncommon in the Cyclades islands, it has many water springs, which make it quite green.
You should stay in Batsi; it is a very nice village and you can go everywhere from here. I would recommend Villa Rena -we had a perfect stay there and the owners, Rena and Johnny, are very nice persons.