I own Excite Truck and love it, and just this week I rented Carbon... I'm still undecided about picking up a copy, the controls seem too floppy, and when in certain control modes, the main menu navigation requires you hold the wiimote vertically, it seems poorly programmed in that sense. Excite Truck wins hands down imo. On the other hand, every single NFS game has won my heart in the end, and I'm sure this one will too, it'll just take some time.
I'd still do anything to replace Rayman with Carbon, no doubt about that!