Reader also had a really good discover quality where I could see stories that were not in my subscribed feeds and because it had a such a large user base, the algorithms got pretty good at showing me stuff I wanted to see. I visit HN for a similar reason, so be exposed to stuff outside of my normal sources. Google reader did this too but with broader scope.

edit: I'll note that if google reader were still around today, its likely the discover algorithm would have been corrupted by bots and trolls and growth seeking managers at google. But back then this hadn't happened yet so it all worked pretty good.