They should've settled on a format to use, prior to rollout.
Here is the States, the FCC and other companies, settled on 18 resolutions and formats which are to be used, and once done, the equipment rolled out to TV stations, and DTV boxes were sold to the public, to be connected to the DTV monitor.
Today, suposedly 3 of the 18 standards are in use: one for 4:3, 720p, and 1080i. That is, unless there was a change.
The only problems we have here, are stations dissapearing, due to a change in their frequency, and possibly interfering with nearby stations on the same physical channel.
In my case, WZMY, 50 (DTV 35) Derry, New Hampshire, had a fairly good analog signal, but their digital one barely works, and sometimes, not so much. Their 35 interferes with a 35 another 30 miles away. End result: losing a station (for a lot of others).
Then again, some are gained. Some religious wacko channel in Worcester Mass (TV 48, forget DTV channel) actually comes in good. Initially, like their analog signal, wasn't clear, and unreliable (as if I have a use for it anyhow).
The BIGGEST DRAWBACK of this system, is it does not error-correct too well. If there's interference, you may lose stations. Other countried adopted standards that would overcome this within reason, to the point that you can have a portable DTV running in the car, and it would work. Try that here, and you'll get squat.
In a nutshell, Greece needed to work out a system first, finalize it, THEN go to market with cunsumers and stations.