Well, that's what I find an interesting discussion point about Raiden. He condemns himself as a psychopath, but I don't think that's true. He does enjoy killing, that much is ingrained into his psyche from his background as a child soldier. But I don't think that alone makes him a psychopath, since at no point did he lose track of his goal (which was noble), or forget his friends and allies. The fact that he is ashamed of the idea that he is nothing more than a murderer alone is telling.
It's not that the idea of wondering whether action games have to force a person to be a psychopath and if they are redeemable people isn't a good one to explore. They truly made raiden a grey character, since you can't say he's entirely a monster but you can't truly call him an entirely noble person either, so I think Kojipro succeeded with him.
The reasons for why Ryu's journey failed where Raiden's succeeded are too numerous to list, but if I had to pick one, Raiden's unfair advantage is that he has a elaborate backstory for KojiPro to build off of that is connected to the MG world at large. The complex was already there, it was just developed further with Rising. In NG1, Ryu's very first act is to attack a nonaggressive ninja, killing him in one strike, noting his youth and merely commenting that he sucked and therefore deserved to die. And that set his character for the next 2 games. There is no compelling reason for him to suddenly question his morality after being alright with them for 30+ years, where as Raiden was always questioning his place in his world from the very beginning.
