Yep, /r/science is about the only default that is ok. And if you've seen a climate change discussion there, you'll realize how painful it is to keep discussion on topic on reddit.

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.