I've driven in northern Greece, a lot over 9 years, the whole of mainland Greece, several other islands and central Athens. The driving is about the same everywhere. I think that whatever the skills, or lack of, of individual drivers, the subjective impression of how bad the driving is is dependent on traffic density. In the UK traffic density is usually much higher than in most of Greece. Crete, outside the cities, is very low traffic density.
There are a few particular idiosyncrasies in Greece.
1 A Greek driver will almost always pull so far forward at traffic lights that he can't see when they change. The driver behind will sound his horn to let him know when they change, i.e. it is more of a courtesy than a "get a move on" which is how it would be considered in the UK.
2 Many roads have a hard shoulder and drivers tend to drive on it or partly on it. A Greek driver will overtake, even when there is continuous on-coming traffic, because there is a sufficient gap between the two streams of cars to allow him to do so. It never occurs to him that a driver in the opposite stream might make the same decision. A large percentage of the excessively high fatal accident rate in Greece, noted by Allan, is due to bad overtaking.
3 Traffic lights will often turn green for traffic going straight on, or turning right, before they turn green for traffic turning left. Greeks cannot stand queues. If there are more than 3 or 4 cars waiting to turn left at traffic lights the next car to arrive will pull past the queue and slew across the front of it, even if he is partially blocking the traffic going straight on. I've even been in a taxi in central Athens where there were 3 lanes that widened into 5 lanes at the lights with an extra lane for turning right and one for turning left. We were turning right but there was a queue in that lane and in the straight on lanes but the one for turning left was empty. The taxi driver pulled into that lane and then gunned across the front of the other four lanes when the lights change.
4 If a Greek driver wants to stop somewhere for a few minutes he will never look for somewhere to park and then walk to the premises he is visiting. He will always park exactly outside the premises even if he is blocking traffic.
I am sure these four behaviours are also observed in the UK but they are not as common as in Greece. You see them every time you drive here.
Warwick
PS If you want to sample a fun ring road try the one round Thessaloniki at night. It's a fast dual carriageway with lots of traffic light controlled junctions. When the road isn't busy, nobody stops for red lights or even slows down. Turning left onto it from one of the side roads is truly terrifying. You risk being hit from either side.