Reddit's mechanism for filtering content is "subreddit" subscriptions. For example if you're only interested in links about movies and music, you subscribe to the subreddits for those subjects. Of course, as Reddit's demographic is geeky, so is its taste in entertainment, so the best that'll get you is geeky movies and music.
The big killer feature that could have helped is user-created subreddits. You could create reddit.com/r/quibb, run it on an invite-only basis, and moderate the submitted content to keep it close to your ideals. Of course, that would only solve the problems of content and membership; it would do nothing to fix Reddit's design.
You're right that Reddit does context poorly. Perhaps you should look at Metafilter as an example of how to add context to aggregated news. Take this post for (an exceptionally long) example: [http://metafilter.com/120387] It has a single main link summarized above the fold, with a large amount of historical context and supplemental links below it. Most posts to Metafilter don't go quite that deep, but almost all provide at least one or two extra links on the subject.