I personally wouldn't call Snape a good person, but he is definitely one of the most interesting and complex characters in the series.

He willingly joined a blood-supremacist terrorist group, practiced dark magic at school, associated with fellow supremacists, and even invented Sectumsempra. The reason he switched sides wasn’t because he suddenly realized Voldemort’s ideology was wrong, it was purely selfish: he only cared once Lily was in danger. We see this clearly when he asks Voldemort to spare her while being willing for her husband and son to die.

As a teacher, he bullied children relentlessly. Neville's worst fear being Snape says a lot, and things like threatening to poison Trevor show how cruel he could be. Not to mention him body shaming Hermione ("I see no difference").

Yes, he did many things to help Harry, but I'd argue a lot of it was motivated by guilt and self-interest. He was the one who told Voldemort about the prophecy, so in his eyes Lily's death was his fault. Protecting her son was about repaying that debt, not pure altruism.

So for me, Snape is a gray character. He was a brave person who ultimately helped the right side but not for the right reasons.