Was the real Ansem a good guy?

Yes, the real Ansem (Ansem the Wise) was a good guy. He was just confused with the idea of getting revenge on his apprentice, Xehanort.

Xehanort had stolen the idea of studying and using hearts for darkness, which turned Xehanort into a Heartless called Ansem and created a Nobody named Xemnas.

Until Ansem the Wise met Riku, Ansem thought revenge was the only way. When he saw that Riku released his inner darkness to help save his friends, Ansem realized that revenge is wrong. Since then, he had been helping Riku fight the darkness.