They dumbed the family down from the original film, especially Clark. The bed gags, taking Ellen to a Burlesque club, running over suitcases, knocking down Stonehenge. Thank god Christmas Vacation put them back on track for the most part!
I think they were dumbed down in this one to exaggerate how out of their element they are. Europe is very different from America. As much as I love traveling overseas it is very overwhelming dealing with a different language, different foods, and different forms of transportation.