It was great... until the other filesystems caught up while it was not under development.
It was great... until it went on a rampage and murdered your data. I kid, but I'm also serious. When it was in current development, no other fs was as efficient with small files, and there's a lot of those on the average Unix system so that's of great interest. But it also was the least reliable filesystem in common use. So it was really never worth using.