Here's how I would compare the Passat to the G6 GT. I really wish I had the 6 speed transmission in the G6. I really miss the 6 speed in the VW. The Passat also feels faster to me and it handles better in my opinion. The G6 holds the road fine, but the VW feels better when cornering hard. The variable ratio steering in the VW is really nice compared to the G6 as is the road crown and crosswind correction. Finally the Passat's suspension feels more refined.
Now, before you ask, "Then why the hell did you lose the VW for the G6," we had the Passat for 5 years and put 128,000 miles on it. It was fun to drive and generally was pretty reliable. However, it was getting to the point where the AC, ignition system, and the computer were acting up and the repair costs were just way too much. Parts and labor on the VW are crazy expensive. We were also ready for something different.
The G6 is a bit roomier in the back seat, a bit wider, and is a more relaxed freeway cruiser. It handles nice and looks amazing. While the fit and finish isn't as nice as the VW, it's more interesting inside. The stock stereo is nicer too. Hopefully the G6 will also prove to be more reasonable to maintain.