By going running around his neighborhood every day after work, John will primarily be improving cardiovascular efficiency and muscular strength. Running is a great way to enhance cardiovascular health by strengthening the heart and improving blood circulation. Additionally, while running, especially if done on varied terrain or with intervals, John can also improve his muscular strength, particularly in the lower body.
While there may be some improvements in speed as well, the primary benefits from consistent running are cardiovascular efficiency and some degree of muscular strength.