I really thought forums lost something when UBB and its clones (vBulletin, phpBB, etc.) became dominant, because those systems only let top-level posts have replies. So you just had forum -> subforums -> posts -> non-threaded stream of comments under each post. It was honestly awful, and for much of the 00s forums just became a chore to read and participate in. And it really seemed to bring the worst out of people and of moderation policies: like, back in the WWWBoard days, if you wanted to respond to multiple comments on a thread, you'd reply individually to those comments, and they'd be threaded in the proper position. But on a UBB forum, if you replied individually to comments like that, half the forum would scream their eyes out at you for "double posting" and often the moderators would threaten to ban you if you did it again. And it also meant that any time an argument would start in a post's comments, that argument would take over any and all discussion under that post. In a WWWBoard system, the argument would be segregated into its own subthread and normal discussion can happen in other replies, but UBB didn't allow that. And when you have megathreads, a lot of times they just devolve into everyone just saying their piece and nobody having any real back-and-forth discussion (and honestly "megathreads" are something that didn't exist at all until UBB came around, because WWWBoard and its clones had no concept of bumping or sticky threads: every post was displayed in descending chronological order with no way to reorder anything)
Honestly, I jumped for joy when Reddit took over as the de facto Internet-wide forums system, because it finally meant we got to have real threads again.