Yes, it is good. (I tend to only use it for sites that already use CSS; for those that don't, the default is almost always good enough.) Even on Hacker News, I use that to do two things: to make all comment text black, and to display dotted lines for the comment indentation to make it more easily to be seen the indentation level (it is implemented as simply a tiling background picture). (For more complicated web pages, I often need to add a lot more stuff to make it work reasonably.)

You can literally do something like what parent comment wanted to do in three (3) minutes, including installing the addon. Stylus is great.