I also use the Windows key, but even then the WHOLE screen animating and changing to a different solid color was super jarring and tiring IMO. I much prefer a small popup like they have now
Click on a pdf? The whole screen turns bright red for a second before loading. Click on a Word file, same but blue. It was hell to use for people sensitive to flashing lights.
I got special permission at work to stick with Windows 7 longer than the rest of the company for medical reasons.
Launchpad appeared for the first time in Mac OS X 10.7 "Lion" in July 2011.
Windows 8.0 launched August 2012.
Personally I think both are inspired by the full-screen launchers of iOS and Android, and not by one another.
The only redeeming thing I could say about Launchpad is that it did not replace Spotlight (unlike Windows 8 Start Menu which was a replacement to the previous start menu)