I too, like the darker is better.
That's the way I always remember Vista, from fresh install.
Quite nice too on totally transparent setting.
For myself on glass, I take it a little further,
by adding the alpha channel, to grab some more of the glass color.
200/255 is always a good starting point for alpha values.
It's an odd relationship with glass color and opacity.
I'll try to explain, from the way I notice.
The opacity CSM settings behave differently than in the image bitmaps, of taskbars, and menus.
With CSM settings with opacity at 0 percent, both the glass color and opacity is reduced.
Where as,
if the bitmaps have 0 percent instead, the opacity is reduced,
but the glass color increases even if there is no glass mask set.