These days on Reddit no one will read the linked posts and the comments are very circlejerky and lower quality. On the other hand Hacker News has mods (mostly just dang lol) vigilantly enforcing their guidelines to maintain somewhat quality discussions.
Another thing is a lot of reposting, bots, and excessive cross posting resulting in a lot of recycled garbage throughout. I miss the days where social media sites ripped off Reddit content, not the other way around.