Do you have any specific examples?
The top bar is also black-ish now rather than the system grey. This looks particularly bad with the new "blue" highlight indicator. The tabs are all square rather than rounded. It all looks pretty hideous.
The overall design is really a mess in 57, although browsing does seem faster.
You might like the "Light" theme, which I think is available by default. That won't do any rounding for you, however.
Labels of background tabs became very transparent. This makes them completely unreadable, as my desktop background is quite dark. So, these tab labels are written with black letters on a dark blue background. So freaking good usability! /s