Depends what sort of thigs you're interested in, really! I would have thought Knossos is a must-see; I must say I was pleasantly surprised by the relative lack of commercialism and the reasonable prices of food & drink at such a major tourist site - though it can get very crowded. Personally I found Phaestos much more interesting; it isn't heavily "restored" like Knossos, and on the day we went we had the whole site virtually to ourselves - the coach trips don't go there and not all that many tourists even realise it exists. Iraklion (Heraklion)isn't a particularly pleasant city, but worth going to for the archaeological musuem. Otherwise most of the places I know in Crete are at the other end of the island from where you're going - sorry. Kalo taxidi!