In response to the increasing use of ChatGPT, this study aimed to analyze ChatGPTgenerated feedback on 126 argumentative essays written by university students in Korean English as a Foreign Language (EFL) classrooms, focusing on content, organization, language and grammar, and mechanics. Results revealed that ChatGPT assigned the highest score to content but the lowest score to language and grammar using a five-point scale. Furthermore, ChatGPT identified recurring writing issues, including a lack of clear thesis statements, underdeveloped arguments, insufficient specific examples or evidence, weak transitions and cohesion, unclear counterarguments, and grammar and syntax problems. These issues need to be reflected in writing instruction for improving argumentative essays. When it comes to the strengths of ChatGPT-generated feedback, it provided immediate and scalable feedback, explicit corrective feedback on language and mechanics, and a standardized overall evaluation that offered a comprehensive view at a glance. However, ChatGPT-generated feedback also had the limitations, including formulaic comments on content and organization, generic and overgeneralized feedback on final suggestions for improvement, and a lack of in-depth analysis of counterarguments and logical flow. The current study has pedagogical implications, offering valuable insights into the interpretation and analysis of ChatGPT-generated feedback as well as recommendations for its optimal integration within EFL contexts.