As shown here and here, among other places:

• The titlebar height is not quite tall enough to comfortably contain the titlebar text.
• The titlebar text shadow is too prominent, and conflicts with the glossy 3D appearance of the titlebar.
• The titlebar button borders and symbols are too high-contrast, and the symbols are off-center by one pixel.
• The window corners are not anti-aliased.
• The notification area icons are too low-contrast.
• The new wallpaper is a little lifeless.

Some positives are that the new Humanity icon theme is a great improvement, and that the font rendering continues to impress.