This UI is a min-maxer's paradise. Which may or may not be what you want.
Of course, I went straight to try to earn the next badge, "Critic", by randomly downvoting the question, and when that didn't get me a badge, downvoting the first answer to it. Well, shucks, I still don't have the badge, and it won't let me downvote comments. So is it broken, or what? Where's my shiny badge?
I'm decently sure that inspiring people to game the system like this isn't the point, but it's what this interface does. That's probably a bad thing.
And I didn't get my badge even after following the instructions, so that seems broken, or you need to explain in the UI that there may be a delay in getting the badge, or whatever. At the moment, it feels wonky and nonfunctional if I do what it tells me, but get no confirmation or payoff.
[Edit: badge has arrived, but it's not letting me undo my downvotes. That wasn't explained, it just told me I had to do it to get a badge. Yeah, new UI seems bad for encouraging system-gaming without also showing the more complex issues.]
[Edit2: this response was because testing something involves finding the ways in which it might break or be exploited. Whether I'm wearing the hat of programmer, security consultant, QA tech or usability tester, the first thing to ask is "what are the failure modes?" - the two points above leaped out at me, as UX issues. I'm interpreting downvotes as "other people performing the same test" rather than "people annoyed that I tested the ways in which this new UI might break" - however, it'd be good to post a comment or answer indicating whether your experience was similar and how it compared: more data points always better.]