I agree with the last paragraph. MGS4 Raiden was a "You WILL learn to love him!" thing.
They tried to make him the new Grey Fox. Everyone loves Grey Fox because well... Hes cool. Hes a cyborg ninja that makes Otacon piss his pants. He saves you from REX and was even in the original 2 Metal Gear games where once again hes a pretty cool guy. Didnt he also make an appearence in Portable Ops?
On top of this, Kojima once even said he wanted to make a game focused on Grey Fox.
In MGS2 "he" comes back for a short while. In MGS2: Substance you can dress Raiden as Grey Fox. In Rising you can dress him as Grey Fox.
I think Kojima realised he killed off a really popular, unique (at the time) character. He screwed up and Raiden was his way of "fixing" that.
Good point, there's definitely an attempt to mirror the coolness of Grey Fox with MGS4 Raiden but like a lot of things in MGS4 it's done in an half-assed way. Grey Fox had mystery surrounding him, a great build up from hearing guards speak of someone killing many other guards, to the moment he slices Ocelot's hand off, to the corridor full of dead guards to when you discover why he knows Snake and who he really is. With Raiden, you don't get to witness his transformation so it feels forced and cheap.
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