He's quickly shown to be a very humble and respectful person. Always eager for input and seeks out information. It's part of his character and is one of the reasons he's so skilled and tactical. Plus, he does slowly come out of his ways a bit and tries to live a little. Both through making friends with the rest of the party and the guild, and seeking more out of life. It ties into part of the general theme about dealing with trauma. Goblin Slayer himself is still improving and moving on, thanks in no small part to the people in his life.

Compare it to other series that often have main and secondary characters that might be assholes or have trash personalities, or even do downright evil things, yet other characters will always inexplicably still like them despite that when there's no redeeming qualities, or they're half-assed ones.

That's actually what I like most about him. You'd think he'd be an angry douche because of all the crap he's seen and been through, but no, instead he's actually quite kind and civil.