The overall aim of software testing is to deliver the error-free and high-quality software products to the end users. The testing process ensures that a software is aligned with the user specification and requirements. In software testing process, there are many challenging tasks however test case generation process is considered as the most challenging one. The quality of the generated test cases has a significant impact on efficiency and effectiveness of the testing process. In order to improve the quality of a developed software, the test cases should be able to achieve maximum adequacy in the testing and requirements' coverage. This paper presents a comparative evaluation of the prominent requirement-based test case generation approaches. Five evaluation criteria namely, inputs for test case generation, transformation techniques, coverage criteria, time and tool's support are defined to systematically compare the approaches. The results of the evaluation are used to identify the gap in the current approaches and research opportunities in requirements-based test case's generation.