Applied power system research is data intensive, often requiring hour-by-hour data on electricity consumption and generation as well as detailed information about technical and cost parameters of power stations. The European Union obliges firms to publish much of this information on a common website, the "ENTSO-E Transparency Platform" operated by the association of transmission system operators. It is possibly the most ambitious platform for power system data globally. However, anecdotal evidence from users indicates significant shortcomings regarding data quality and usability. This paper provides an introduction to and an assessment of the Transparency Platform, helping researchers to use it more efficiently and to judge data quality more rigorously.