In this study, we use Mathematical Quality of Instruction (MQI), a content-specific observation framework, to examine the mathematical quality of instruction of three focal lessons in order to examine the instructional aspects illuminated by this framework as well as discuss those aspects not captured by MQI. While prior work provides evidence on the validity and reliability of the MQI measures, no prior work systematically explores the strengths and limitations of MQI in capturing instructional quality. Our analysis points to the affordances of MQI for highlighting differences within lessons across instructional dimensions related to the mathematics of the lesson, as well as for comparing across lessons with respect to the depth and quality of the mathematics instruction provided to students. We discuss how the depth of information provided by MQI may guide instructional improvement efforts. In addition, we explore three categories of instructional aspects not highlighted when examining instruction through the lens of MQI, addressing areas in which MQI in particular, and observation instruments in general, might be limited in their capacity to support teachers in instructional improvement efforts.