The interview was tough as EPSO is tryibng to evaluate canditates from different perspectives. I was being interviewed for an AD7 position (professional/ expert), during a competition organized by the European Commission.
I was an outsider, ie. a lot of people from inside EC trying to climb the professional ladder - means tough competition.
My impression was that they put too much emphasis on behavioural competencies and less on professional ones. I check the member of the Board before and none had experience in my field so the question were not really 'at the edge' of my knowledge.
I think once you are in, it is easier to stay in. If you come from the outside, you are less familiar with the 'environment' and you might not be the type they want to fulfill the task the give you.
My advice : familiarize yourself with the EC if you want to work there (e.g trainships, temporary positions etc)