I'm sure they're an excellent tire but still will be a compromise over dedicated winter tires.
Though, at least to me, the WR G4 isn't more than a ~10% reduction off the outright winter performance of the top-end Hakkas that Nokian sells. (Have had both models of tire.)
While ice performance of the WR G4 isn't nearly what a dedicated winter ice+snow tire is, I've been duly impressed with the non-ice performance of the WR G4. It's gotten me through most of the ugly winter weather that can be thrown on the roads. Have been in a foot of snow, snow over ice, slushy mix that got frozen with several inches of snow on top, "wintry" mix, sleet "marbles" on top of slushy mix, and so forth. And these tires have handled it all darned well. A half-step down from the Hakkas, but hands down seriously more capable than
any ostensibly "all"-season tire I've ever used. The compound that Nokian has selected for the WR G4 is quite capable of handling all-year usage, including quite a bit below 0ºF.
Am on the third winter of the things and into the first couple months of the fourth year of year-'round use. Good tires. Wish those 19" sizes were priced similar to what the 17-inchers go for, but that's about my only gripe.
I, too, hope the G5 is equally competent in the nasty stuff.