The few articles that I've read on fivethirtyeight so far have all been of excellent quality. While Krugman might have some ideological grievances with this website, there are no concrete flaws that he can actually point to, therefore his criticism remains very abstract, and for practical purposes moot. I would take his criticism a lot more seriously if he can pick out a handful of articles published on fivethirtyeight, and show that their conclusions have been refuted by various expert researchers in that domain (while saving the data).