The only negative thing about 18 teams is that for National team players, they would get really tired. Playing the domestic league, Cup, Champion League/Europa and of course for the Ethniki would get the players a bit more tired and with a better chance of injury.
England plays way too many games in their season. I mean they play even during holidays. This is why I believe they never can perform well for their national team. Players are not robots they need to rest too.
As a fan, 34 games would be better I suppose. But if they do this, will they still have the playoffs for teams in position 2 thru 5? Then they will play another 6 games on top of that all the way thru June, so that is 40 games! I don't like that and I think its quite ridiculous!
Just have a baraz 2 knock out games, for example, #2 plays #5 and winner meets #3 vs. #4 winner and thats it.