Win7 had translucency, and it looked way better than Win8+. Vista looked meh because it overdid it initially, but Win7 dialed it down (mostly with "frosted glass" effect) in most places to where it didn't impede contrast, and added various ways to highlight text in places where it was directly overlaid over glass.

Judging from the demos, Apple's version is even more translucent than Vista, so I have no doubt that it'll be bad.