The mix is an essential part of the music production process, which has an important but poorly understood impact on the perception of a record. Little is known about which aspects are the most important, and how to acquire such information. In this work we collect, annotate and analyse over 1400 reviews by trained listeners on 98 mixes. We assess which instruments, types of processing and mix properties are most apparent when comparing mixes, and explore which challenges arise when interpreting these comments. The benefits of using such unstructured data are discussed and a methodology for analysing it is proposed.