This study is an illustration of the value of appraisal theory in studies of writing assessment. To demonstrate its functionality and value, appraisal theory is used to examine rater variability and scoring criteria through an analysis of the evaluative nature of rater comments. This allows an exploration of the values raters bring to the scoring task of rating second language writing proficiency. The written comments of three raters scoring the same sixteen writing tests were analyzed through appraisal theory and correlated to each test score. The analysis of the comments suggests that textual features external to the scoring rubric influenced raters' scoring decisions. The findings shed light on raters' perception of the construct of "good writing" and show how raters bring their own interpretations to the rating task. The findings also suggest that there may be unidentified shared rater values, as was evidenced when all raters awarded the same score but disagreed on the quality of specific features of a text. These observations may have implications for rater monitoring, rater training, and scoring rubric revision. This study illustrates that appraisal theory may offer a systematic means to analyze rater comments as they relate to the rating process.