erm Europe is a big place - you're bound to lose detail trying to cover such a large area. The most useful combination of detail and coverage is in the 1:200k or 1:400k maps - these cover only regions within countries (although I guess small countires may get their own map).
Yes - 1:500k is asking a bit much for there to be much detail when it gets a bit populated - I have used worse succesfuly in some countries - but that was because generally there was not much to put on the map in the first place
I second Andym that a map at 1:200k to 1:400k is most appropriate for road touring