I suppose that's subjective, because to me it looks distracting and tacky. I want the window chrome to be present, opinionated, yet consistent and plain. This is one of the many Tahoe-isms that violates the latter two. It's visual noise that detracts from one of the most basic utilities of the UI, which is to simply hold my applications in a regular, cohesive, predictable manner.

Maybe it shouldn't irritate me, but it's the first time I've encountered it in 30 years. I'm all for change and trying new things, but this doesn't feel like progress.

It is intentional - it was explained at WWDC. And it looks good.