Best Single-Player FPS Games With Perfect Progression, Ranked

First-person shooters are awesome in many ways, but progression rarely seems to be one of them. If we remove RPGs with shooter gameplay like Borderlands and multiplayer modes, we aren't left with all that many single-player FPS games that actually feature progression in a way that warrants a mention. Typically, progression amounts to "I have bigger guns now," which is satisfying but not particularly interesting.