You hit the nail on the head with reddit's upvote/downvote system: folks should be upvoting legitimate contributions to discussion, but instead they upvote funny, clever comments and downvote anything that contradicts or offends their existing views. I was active on reddit for about four years and watched its decline. The jokes and cleverness increased exponentially. Meanwhile I got mercilessly downvoted and criticized for pointing out unpopular things that are nonetheless true, e.g. that the middle ages were a period in which large technological and social strides occurred, that 5/3/1 is not the ultimate weight training program, that the Meyers-Briggs personality index is not much more reliable than astrology. I finally gave up and quit when a board moderator personally attacked me for noting that there are age related declines in your physical capabilities.

One of the current reddit front page items is nothing more than a photo that's linked as "WTF." The guy couldn't think of one single descriptive word to write for it? Yet it made the front page.

My limited experience suggests that reddit's credibility fell in two big waves. First, the Digg migration. Second, an influx of children from 4chan.

If it helps, you can vastly improve your reddit experience by immediately removing from your subscription list /r/pics, /r/wtf and /r/funny. If you want to eliminate the circlejerks as well, unsubscribe from /r/atheism, /r/politics, and so forth. Subscribe to topical subreddits like worldnews, science, and some for your area.