As is typical in Greek, the first participle ("going") may well take on the force of a command ("go!"). However, and please note this carefully, the syntax of the passage (as noted by Stan Porter) "retains the focus upon the making of disciples, which is at the syntactical heart of this command because it identifies the lexis of the finite verb as Predicator." Porter also insists that "There is nothing here that minimizes the Great Commision to a suggestion." Porter, therefore, renders the Greek as follows:
Going, therefore, make disciples of all nations.
Please, please don't repeat the silly argument that if we don't render the first participle as "Go!" we are reducing the Great Commission to a suggestion ("The Great Suggestion"). I call it the Great Assumption. In other words, Jesus assumes we are all going somewhere (ideally where he is leading us). As a good friend of mine puts it, "Life is a mission trip. Take it." I would add "regardless of your location and your vocation." But do not think you can be on mission for Christ only if you "deploy" overseas.