It is simple but simplicity does not preclude depth. Ghosts of one's past can consist of many things. An action one feels guilt about, perhaps something that was a scarring experience like an accident or the death of a close person, all of these and more can amount to the haunting "spirit" that can really strongly affect one's outlook.
Not an animator, but I'd guess that the effort that went into this was neither too little or too much given the topic, but rather it touches on the topic without spending too much time on it which is easily just as irritating as not spending enough time on something.
The audio gives good ambience as well