It's fairly subjective. Call of Duty is an incredibly immersive game and though the online play becomes overly competitive at times, it provides a great amount of stress relief and venting personal frustrations by, in some sense, allowing access to what is, in most cases, a significantly cooler life, allowing them time to relax some parts of their brain as well as built up muscle and nervous tension. And in that sense you could equally argue that books are a waste of time, despite enormous psychological benefits from reading. Video games provide a very similar function, as well some level of training in fine motor skills, accuracy of hand movements in correlation to visual stimuli, constant assessment of your surroundings, and rapid decision making, which most people desperately need. I wouldn't be surprised to see MS and ALS patients benefit to some extent, at least with use of their hands, from playing FPS and other fast paced games regularly.