[pax]

Как-то так:

public class LevelLoaderScreen : MonoBehaviour
{
    public string levelName;
    public Texture2D loadingScreenTexture;

    private AsyncOperation _loadingProgress;

    public void Start()
    {
        DontDestroyOnLoad(gameObject);
        DontDestroyOnLoad(loadingScreenTexture);
        _loadingProgress = Application.LoadLevelAsync(levelName);
    }

    public void OnGUI()
    {
        var screenRect = new Rect(0, 0, Screen.width, Screen.height);
        GUI.DrawTexture(screenRect, loadingScreenTexture);

        if(!_loadingProgress.isDone)
        {
            var labelStyle = new GUIStyle(GUI.skin.label);
            labelStyle.alignment = TextAnchor.MiddleCenter;

            GUI.Label(screenRect, "Lading: "+(_loadingProgress.progress * 100).ToString("000"));
        }
        else
        {
            var buttonRect = new Rect(Screen.width/2 - 80, Screen.height/2 - 30, 160, 60);
            if(GUI.Button(buttonRect,"Press to continue"))
            {
                Destroy(loadingScreenTexture);
                Destroy(gameObject);
            }
        }
    }

}