The subtle color enhancements are nice (nothing like lowering contrast to make things look classier) but the button hovers appear broken.. that was an important bit of sparkle in twbs2 I hope 'twas just an oversight.
The hovers work, but they are so subtle you will barely notice it. I had to get very close to my monitor to notice on colors other than the default greyish white.
You can see a slight darkening around the edges; it's easiest to see on the default gray button. I agree: this needs to a be a stronger indicator.