WaPo‘s Tom Sietsema has threatened to kick a four-star performer off his list in the past, but this year he finally did it. In one of his boldest dining guides to date, the critic booted CityZen from the 2010 edition. It was just one of many shake-ups in this year’s guide.

I’ve been trying to reach CityZen chef Eric Ziebold for comment, but we haven’t connected yet. Perhaps he doesn’t want to talk about it, which I’d understand. I also asked Sietsema if he wouldn’t mind explaining the restaurant’s fall from grace.

Here’s his e-mail response:

As I mentioned in the introduction, not all the usual “best” restaurants would be (or could be) included this insider-themed issue.

In the case of CityZen, I visited twice just before my deadline, once at the bar and again in the dining room. While the service there has never been better, and I love the dining room, I thought the cooking this fall was more subdued, less soulful — indeed, less interesting — than I’ve come to expect from Eric Ziebold. In fairness, the chef was away from the kitchen when I ate in the formal dining room (he was sick, actually). Even so, I think a restaurant at that level should act and taste as if the boss were present even if he’s not.

In the end, I think two factors played into CityZen’s dismissal. One was Sietsema’s narrow focus on trendy restaurants, which, as he noted in his introduction, “means you won’t be reading about all of the area’s better-known addresses or popular standbys for sushi, steak or pizza. Chances are, you already know about them.”

But CityZen’s kitchen apparently sliced its own finger off, too, by taking the boss’ absence as a chance to let its guard down. Either one of these factors — the theme or the off-day — probably wouldn’t have been enough to sink CityZen. But together, they felled a giant.