I have driven in Europe in six different trips, and in all the countries you have mentioned. Highways are very good. It is quite easy to get from one town to another. However, driving in old town areas could be difficult as the roads are narrow and may be in cobblestone. In general, driving in Europe is quite enjoyable and is a very good way to explore the continent.
Something you may want to pay attention to:
1) Most of the cars in rental comapnies are stick shift. Automatic is expensive and sometimes not available.
2) in most countries there is no charge to return a car to another location within that country, but it costs a lot if you return it in another country. So it is better to plan your trip carefully.
3) If you rent a car in Western Europe, you may not be able to drive your car into Eastern European countries. You will need to tell the car rental companies the countries you plan to visit to make sure that you are covered by insurance.
4) GPS is only provided for additional fee, and it is not cheap. I have been trying to get by without renting GPS.