Do you mean Crete in Greece?
I'm from Chania in west Crete. There is a very good dive store (
http://www.chaniadiving.gr/ ) which caters all levels from snorkelers up to trimix and rebreather diving.
Their usual dives are some very easy (OW level) and nice caverns and rock formations with swim throughs etc.
There is a also a very nice easily accessible "cave". Entrance is at 12 meters then you pass through a wide (but still hard overhead) passage ~10 meters long and then the cave opens up to maybe 30m tall and some 300m long filled with breathable air. Water in the cave is about 1.5m deep, hence you actually walk around. It is called elephant cave. In it you can see petrified leftovers of the skeleton of a prehistoric elephant/ mammoth as well as very nice stalactite and stalagmite formations.
On top of these, there are more advanced sites like caves, deep ship and airplane wrecks from WWII etc.
Generally the conditions are swimming pool like: clear water, no currents, not much fish, though there is some macro life (nudies etc) if you are careful enough.
I haven't dived anywhere else around the island, but I've heard that diving in the central part of the island (Heraklion area) is more lively (more fish). In the east part of the island (Agios Nikolaos area) there are supposed to be the ruins of an ancient city/village submerged so you can dive through them - but I haven't been there either so I can't comment.
South side of the island has even more crystal clear waters and nicer/wilder terrain, but fewer operators dive there.
If you come let me know, so maybe we can meet/dive or have a drink together!
Regards