public enum GameState
{
    MainMenu,
    InGame,
    GameOver
};

class MyGame
{
/// snip
protected GameState gameState = GameState.MainMenu;

protected override void Draw(GameTime gameTime)
{
    /// snip
    switch(this.gameState)
    {
        case(GameState.MainMenu):

        break;
        // same for all the others

        default:
            throw new Exception("oh noes");
        break;

    }
}


}