Santorini is the east half of a volcano, more or less: slopes up one side, cliff on the other. The other half exploded. It isn't really a resort destination like other Greek islands: it does have beaches but they're mostly black, volcanic sand; other islands are prettier. What it does have is stupendous views out over what remains of the crater, great sunsets, and some good ruins dug out from under the volcanic residue of an explosion about 2500 years ago. (They think this may be the one that destroyed the Minoan civilisation on Crete, and may also be the source of the legend of Atlanitis.) There are good hotels and probably good restaurants too, though the ones I ate at last time I was there (six years ago) varied from okay to crap.
IaP's hotel looks wonderful. This is the one I stayed at, also very good:
http://www.tripadvisor.com/Hotel_Review-g18943 3-d234210-Reviews-Pantheon_Deluxe_Villas-Santo rini_Cyclades.html