You would like to have a twin, which would help you to pass the puzzle? This mod will show how to use a time machine to create his counterpart from the past that will help pass the puzzle.
While the textures and visual design are neat and polished, almost everything else isn't. The mechanics are buggy and often lead to repeated frustration. The mapping is also very, very questionable. (The glass around the elevators aren't supported by anything, lazy geometry in certain places, and even the use of textures that don't fit into the game at all, like a placeholder "GlaDOS shutdown" down.) The 3d skybox is also very clunky, it would benefit from using the same method as Valve's maps (Building the outside area around the playing field), rather then trying to do this as a shortcut. For instance, you can see bits of the elevator shaft hovering in the skybox, and props like cubes look much too large when viewed through the 3d skybox.
The puzzles are interesting, and the concept is solid, but it's so very unpolished that it ends up looking really, really lazy. There isn't much of a story, and what little there is just serves to confused and befuddle Portal 2's original story with out of character scenes.
If it were cleaned up a little, and the story was either altogether deleted/rewritten, it would get a much higher score. As it stands it's a 1 hour, interesting little brain teaser, but don't be suprised if it leaves a sour taste in your mouth.