Slashdot attempted a redesign, but there was a revolt (the slashcott) where everybody refused to discuss anything except for their dislike of the redesign, and - after a week or so - the site relented and didn't go ahead with the change.

The real cause of the decline of slashdot, in my opinion, was the corporate buyout and departure of CmdrTaco, Hemos, and the rest.

For what it's worth, the site is still going, there's usually at least 1 story with >100 comments on the first page, at least when I've taken a look.