I've never seen it that bad until today but when a reply thread goes for a long time it starts pushing replies into tighter and tighter columns. Eventually you're reading English in a strange Far East format
The fact that most threads don't go that deep is the only reason that we hadn't fixed it before. It's a hard problem to solve. Both Hacker News and Reddit have links to read more. I believe Paul Grahams reasoning was that very rarely to productive conversations happen that deeply and so hiding them and/or making it harder to view was actually a benefit to the community.
I'm not so sure that's the case here, at least not that I've seen.