In MGS2, I think most people agree that Raiden was a shitty character. A whiny, confused, easily manipulated rookie, with a really jarring appearance.
MGS2 was a pretty good game, it brought great advancements in the gameplay. But to be fair, the story had many problems. And they did not start and end with just Raiden. I've played through MGS2 many many times, and I still barely remember what the hell the game was even about. The Big Shell was being held by terrorists with a nuke, but it it turns out that something about the Big Shell being a recreation of Shadow Moses to train another soldier to replace Solid Snake which was the purpose of Raiden, but then it turns out the entire thing was an experiment by an AI to control global human social consciousness and the progression of human historyFFFFFFFFFFFFFFF.
The story in MGS2 was just overwhelmingly full of shit, and poor Raiden was not up to the task of tying the hackneyed disaster writeup by Kojima together.
Raiden returns in MGS4 as a battle-hardened cyborg ninja, as a character he was just a lot better this time around. It was disappointing that there wasn't much interaction with him, I was at least pleased that he did seem to have made a turn around.