[en] The critical issues, evaluation and comparison of two inertial fusion energy (IFE) reactor design concepts developed in the Prometheus studies are presented. The objectives were (1) to identify and characterize the critical issues and the R and D required to solve them, and (2) to establish a sound basis for future IFE technical and programmatic decisions by evaluating and comparing the different design concepts. Quantitative evaluation and comparison of the two design options have been made with special focus on physics feasibility, engineering feasibility, economics, safety and environment, and research and development (R and D) requirements. Two key conclusions are made based on the overall evaluation analysis: (1) The heavy-ion driven reactors appear to have an overall advantage over laser-driven reactors; and: (2) The differences in scores are not large and future results of R and D could change the overall ranking of the two IFE concepts