Is Slytherin good or bad?
Yes,
Slytherins could be snide and cruel, as Harry Potter can vouch. But we think being a Slytherin does not necessarily make someone a bad person. ... To us, Draco is proof that Slytherin was not a breeding ground for evil and Dark wizards, but wizards full of flaws and desires just like anyone else.
Are there any nice slytherins?
Canonically, there
were only three good Slytherins: Horace Slughorn: He was a good person at heart, was against Voldemort and the Death Eaters and fought at the Battle of Hogwarts against Voldemort. However, he had his biases.