Firm, but not crashy, is probably what I'd guess it is like.I can absolutely state that the ride is not "much harsher" for the B6s on the Cruze. It is stiffer, but it feels sporty, more like a BMW, not harsh by any means. I find that I can now run the tires at OEM sidewall pressure and the ride is quite nice.
I have the B6s on my '81 Camaro, and despite being a double wishbone and leaf spring setup (granted, all the suspension is new, but is on Hotchkis springs front/rear), it rides absolutely excellent.