One thing I appreciate about Slashdot versus HN is more people with expertise in a broader range of science and engineering fields. HN is very good in certain areas of technology and business, but has relatively few civil engineers, physicists, climate scientists, chemical engineers, astronomers, etc., so the comments on those kinds of stories end up drifting more into speculation. On Slashdot, there are usually at least a few really good comments on the story from people with expertise in those areas.