My opinion on the matter is:
I prefer a white (well just some bright color, might be gray) text on black background, just like it sounds most other people here does. I'm starting to get used to the site since the brightness have been lowered a few times, both on the site and my monitor. So now I don't care that much, I just hope the admins will get a black theme ready in a couple of weeks (don't know how much it takes to make such a theme).
Lots of things apart from the color scheme have of course changed, and I'm very impressed with most of them. The site still looks like it's in some early beta version, but if I'm not very mistaking (don't think there have been an "official" comment on this matter) this is some kind of big beta test with lots of testers.
One thing I hope will be fixed soon is the dropdown menu, which I really hope they will get fixed soon. One of the big problems I had with the old GDNet was that the menu at the top was a mess, after a couple of weeks I knew where most stuff in the menu was, but it looks very bad to first time visitors. The dropdown menu made a very big improvement to the "ease of navigation".
Another thing I really like is the new source code boxes, I don't know what it's, but they just look much better. It might be because the background aren't going from something like 0, 0, 0 to 255,255,255 (with 255 max, in RGB format), but more like 200, 200, 200 to 255, 255, 255.
I also like the way if any new messages is in a forum is indicated (red ball / bright blue ball). It is much easier to spot the difference.
So for a conclusion:
I think the new design, with some time, will far surpass the old one, especially in usability and eye-candy (yes, admit it, it does matter.