I thought you were joking, since the last time I saw craigslist it was hilariously awful looking.
But, actually, it seems super clear and easy to navigate and certainly doesn't hurt my eyes. I am really surprised that either my usability/design standards have dropped so massively, or craigslist has improved enough without an overhaul.
Craigslist has slowly changed over the years with little tweaks here and there. It’s really fun to go through the Wayback Machine on it when people bring it up as an example of something that hasn’t changed.
It's a thing of beauty. Simple, functional, information dense, logical layout. I don't use craigslist, but pulling it up, it is immediately obvious what needs to be done and how to do it.
I've never had any problem using Craig's List and it just works. There are no hamburgers, no material design, the dropdowns look like dropdowns, and the links look like links. I love Craig's List! It's one of the only shopping/marketplace websites I don't dislike.
My philosophy is that if you want it to have fancy CSS and skeuomorphic buttons, use a CSS extension and make your own CSS for it. Even better - use a browser that lets you edit a page's CSS in WYSIWYG (if there are any).
If Craig's List was suddenly revamped and looked like Amazon or Newegg, I would no longer use it.