I gotta admit... I didn't like Riku during the first Kingdom Hearts. I thought he as a D*** towards Sora.
He was fine in the beginning til after traverse town pt 2 and after that til after you beat him when he's possessed by xenhanort he was a dock but not on sasukes levels and at the end of the first game til now riku is the best developed character in the series. Chain of memories, 358/2 days, 2, and dream drop showed his development and how much he really cares about sora and his friends. Plus his redemption was perfectly done and he is so much more likable even at his worse riku is.