This is mostly because Reddit's choice of default subreddits are poor (and cater to the lowest common denominator): http://i.imgur.com/9FLPgsW.png
You have manually curate the subreddits you want, unfortunately.
You have manually curate the subreddits you want, unfortunately.
Presumably this isn't entirely a choice: I would expect a good subreddit to get worse if it was made default. (And I've heard that /r/atheism got better when it was made undefault, but I haven't actually looked.)
What we're seeing right now is the after effects of popularity.
I remember going to reddit and thinking, damn these comments are loads better than slashdot. I don't think I can contribute anything interesting, these people are sharp so I won't post at all.
Might have just been me but there is a marked difference in tone on the site.
I would almost suggest replacing /r/gaming with /r/games, which is a 100x more intelligent subreddit with actual discussion (due to proper moderating and disabling of thumbnails), but I would hate to see that subreddit become toxic because of front-page publicity. It really depends on how dedicated its moderators are up for the task.