The gameplay allows you to switch between the two protagonists at any time just presing one button. And you will have to do so, as the light will kill Dr. Shadow and the darkness will do the same to Mr. Light.
In addition to this 'small inconvenience,' there's the fact that Mr. Light can run and jump, as you find in traditional platform games, while Dr. Shadow can only walk... Though he isn't affected by the laws of gravity and will always stick to the ground.
Of Light and Shadow is a platform game that includes puzzle elements, and it not only has a very original and fun gameplay, but also has very good graphics as well as an interesting story starring two charismatic characters.