Went in Crete island of Greece 2 weeks ago, no problem. Third years there with drones. No issues with customs or security, same process as in any other European country. As you said, there are some specific critical areas where it is better not to flight in addition to the usual one. You have maybe to take more attention, maybe more in summer, about any kind of flying object (parachutes driven by boats b.e.) near beaches and as there could be sometimes helicopter flying fast and low. Also good to check (like on UAV Forecast app) before planning to fly for any nearby airports as they are NFZ by law but DJI don't mark them as NFZ.
But apart from that, all positive, beautiful country.