Digg was cool for its time but it was way overly simplistic. The frontpage was dominated by a really narrow set of power users because of how the system worked and the comments were single threaded. It was kind of a hot mess.
It is both crazy that K Rose missed out on selling it for $250 million and that's all it was worth. Had he played his cards right, it could have been Twitter and valued at tens of billions of dollars.
If you want to get into great sites that I miss, I really miss Reddit from 2005-2010, maybe a little later. Do I get a prize for using Reddit when it had no comments? The programming related discussions were good. HN's too ideological and big for them now, and r/progamming is a clusterfuck of people being assholes to each other and talking about shit we were arguing about 15 years ago.
Those early sites had a feel that I can only imagine the pre-Eternal September net had for older people.