When reviewing an Angular developer's portfolio, pay attention to the complexity and diversity of the projects they have worked on. Assess the quality of their code, user interfaces, and the overall functionality of the applications. Look for developers who have experience in building applications similar to the one you envision, as it indicates their ability to meet your specific requirements. Additionally, consider the feedback and testimonials from their previous clients to gain insights into the professionalism, reliability, and satisfaction of their clients.