This paper presents a novel framework for analyzing video game interventions targeting anxiety and depression in randomized controlled trials. We classify games based on their therapeutic approach and analyze their design features using Laine et al.’s design principles taxonomy organized by Plass et al.’s engagement dimensions. Through case studies of Hit the Cancer and Bejeweled, we demonstrate how specific game design features foster different types of engagement. We then present and discuss the most frequent game design principles and engagement identified in five different casual games analyzed.