To get back on topic, let me throw in a few experiences...

1) Roads in Europe are a little bit more narrow and this takes a little getting used to. When road work is being done on the autobahn, for example, the road crews will further narrow the (for example) three driving lanes into three lanes driving where two lanes used to be (I hope that came out sensible).

2) I usually always get a stick shift. The last time I rented a car in England, however, I went with the automatic, only because I wanted to concentrate on driving on the left side of the road (which was already somewhat uncomfortable) and not have to also 'learn' how to shift with my other hand, drive on the other side of the car, etc.

3) Some rental car companies will only allow certain types of cars into former eastern bloc countries. The last time I rented a car in MUC, I was given a MB A180, but had to sign a paper saying I would not drive it into Czech, Poland or Italy.

4) Become familiar with the road signs. They are not altogether different, but it takes a little getting used to. Obey the pedestrian in the crosswalks areas.

5) Parking spaces are significantly smaller than in the US. Be prepared. I usually just parked the car in town (like at the bahnhof), and then public transport around town.