One of the earliest examples of a platformer meets FPS, Jumping Flash broke new grounds. It's weird worlds and emphasis on collecting make this easily one of the most charming FPS' and one of the few geared toward a younger player base. My first example of playing a game with a New Game plus, which I loved discovering and kept me playing. Vastly outdated now, JF is a cute little time capsule of FPS experimentation. Oh, and the soundtrack is beyond good!