As soon as politics touches upon a topic, forget about impartial information on Wikipedia, because there is a serious risk that you will be presented with high-quality, convincing propaganda. That means: Anything related to history, biographies of people who ever had any kind of political controversy about them (i.e. not only politicians), descriptions of political ideologies and viewpoints, world conflicts, anything related to sociology and psychology... Even parts of IT, like when it comes to the GNU/Linux naming controversy and the like.
I assume you read Wikipedia in multiple languages. If so, in your experience, is the above equally true for all the different language Wikipedias you read, or more for some than others?