My first impression of the new logo is that it looks like someone took a nice color logo and ran it through a 1990s black-and-white photocopier. It's that same pure-black chunkiness with edges that aren't smooth and fine details that blur together. It's fine if that's what you're going for, it's just not my cup of tea.

More problematic I think is your change to the "standard template" for sites. You replaced the old graphic (a logo and the words "Stack Exchange") with the new logo all by itself. The logo is just a couple of stacked lines and bears more than a passing resemblance to the standard "hamburger menu" icon. It's even up in the top corner where you'd expect a hamburger menu to be. I did a bit of hallway UI testing with folks who I know don't use this site, and 2 out of 5 of them tried to click it like it was a hamburger menu. The old design didn't have that problem both because of the color and because the accompanying text made it clear that it was a logo and not part of the UI.