Perhaps it's not a prevailing opinion, but I really don't like the new theme. The colors are hard on the eyes, everything's either too small or way too big, and I hate how ancillary information is displayed as a sidebar when I'm browsing the front page. I'd prefer stuff like that at the bottom.
That said, there are a few redeeming qualities to it. It's a good idea to put groups on the front page, rather than force the user to click on a separate tab; most of the time, I forget I'm even part of them due to that. As well, while I probably wouldn't use it on a desktop, with some modification it'd look great on a mobile device.
These are just my candid opinions, of course. I really appreciate the effort you guys are putting into it, I'd love to see where it goes; just so long as we retain the option to use current "classic" theme.