I personally like the 'less' is 'more' type feeling I'm getting from the forum. It makes it easy to read.
What I would try and improve would be to make all the white spaces a softer color. I think that the white is too harsh after all the soft greys around it and it could do with a light grey or perhaps a light grey noise. (so that it's consistent with the background, but different)
Aside from that, as I said above, I like the 'less' is 'more' design and if you change the white to something softer it'd be a 5/5.
The on/off icons are just squares. While this is minimal, I think if you're going to be simple, you should remove some of tge gradation on them. If they were more flat, it may match better with the rest of the forum.
I'm not a fan of the double divider between each category. I think just the category name would suffice.