At the 75% cocoa level we begin to experience more of the natural flavour of the cocoa bean and lose some of the sweetness offered by the sugar which normally accompanies cocoa solids and cocoa butter. The problem with generalising the flavour profiles offered by chocolate at the seventy-five level is that there is no set ratio for cocoa solids, which provides the acidity and cocoa butter which adds to the mellowness and creaminess of the texture. It is often the case that a 75% chocolate will be milder than a 70% for example.
When trying to find the perfect 75% chocolate bar it is also worth looking at how much sugar is present by looking at the ingredients and also exploring if vanilla is added. This often gives it a sweeter flavour and masks some of the natural acidity offered by the cocoa. If you are adamant that you would like to buy a 75% bar but it fairly bitter or intense then look for vanilla in the ingredients and the words bitter or intense in the descriptions.