/r/space was a great place. It was full of smart people talking about everything from robotics to astronomy to physics. Then, they made it a default sub. When they did that, I deleted all my accounts and bailed. The last time I looked over there was about a month ago, and man, it was sad. memes, low value content, re-posted images, and more importantly in my eyes, not nearly as many comments as before. And the comments they did have were all what I consider low value. Post like "repost!" and jokes and memes in response.
I've got a few friends who are still active on Reddit, and when I look over their shoulders to see what is going on, I'm not impressed. Reddit went through a serious demographic shift right after the Digg Migration, where the site got popular way to fast to absorb the new people into the culture. This is when "Le Reddit army" became a thing everywhere.
The only place I really 'internet' any more is here, slashdot (and that place is a whole post in itself) and a big astronomy forum site. That is about it. And I used to drop 30+ hours there... now I go there once a few months if that.