Effective peer code review in collaborative software development necessitates useful reviewer comments and supportive automated tools. Code review comments are a central component of the Modern Code Review process in the industry and open-source development. Therefore, it is important to ensure these comments serve their purposes. This paper reflects the evolution of research on the usefulness of code review comments. It examines papers that define the usefulness of code review comments, mine and annotate datasets, study developers' perceptions, analyze factors from different aspects, and use machine learning classifiers to automatically predict the usefulness of code review comments. Finally, it discusses the open problems and challenges in recognizing useful code review comments for future research.