I've always liked Raiden. He starts off an annoying shit in MGS2 though but grows in to a stronger and more appealing character once he understands the amount of shit that occurs in the story. Reminds me of Tidus in FFX. Annoying and ignorant at first, becomes a stronger and more confident character as the story progresses and he clues on. I even became sympathetic upon the full realization of how fucked up everything is for them.
With MGS4, Raiden went through something even worse than MGS2's events during the capture by the Patriots in-between it and MGS4, so I understood his turnaround in and around MGS4. Plus the love of his life fucked off with the guy he thought was his commander in MGS2. Obviously he wasn't aware of why this particular thing even happened but I'd go insane as well. Overall he suffered enough bullshit that it would change anyone.
With Rising, by then Raiden embraces that he will always be an outcast and can't live a 'normal life' (as he says in the Codec he tried getting normal jobs and shit but everyone was scared of him cos they could tell he wore prosthetic skin), so he tries to get by on what he knows best. He still has his wife and son so his life is good as it could be given his circumstances. Obviously the events of Rising resonate with him so much due to his own childhood as some crazy child soldier, so it makes him more believable.
Not too keen on his switch back to Jack the Ripper but I guess given the circumstances in the story, he needed to reach within himself to pull that personality back to succeed in the mission. Raging out that people still want to exploit kids for combat purposes made him rage out I guess.
He's got a good arc IMO though I'm not sure where it could go now outside of just going around saving children and stopping evil corporations and shit. As a character, how can he progress? I dunno.