It has been a godsend. The new design is bad in all the ways that most modern designs are bad: lots of needless padding, ads everywhere, poor information density. After they effectively killed third party apps, old.reddit.com has been the last bastion of a design intended for power users.
It's the only thing usable for mods.
The new interface intentionally hostile, doesn't provide a way to read the entire thread, replies in a compact way.