To me, reddit seems a great way for a community to reinforce groupthink.
Instances I can think of are forums for motorcycles, cars, photography, and certain tech forums. The ability to nest down by topic rather than having one giant page for say all of BMW cars is what I like about forums. /r/BMW is basically worthless to me as it's just picture sharing. I also dislike reddit because it's hard to remember a name constantly. It's easier when there's a little profile picture next to the name. You go, "oh yeah, that guy. He's helpful." You remember those posters more often.
Never been a big fan of reddit as it feels pretty shallow in comparison to forums and getting to actually know fellow members decently feels rare.