The v8 is unrefined, but effective at both propelling the car at a high rate of acceleration, and emptying the fuel tank if driven hard. It returns between 14 and 15 l/100k in the city (more if pushed) while highway economy is surprisingly good at between 9.5 to 11 l/100k.
The 4 speed auto is a very low tech device that certainly lets you know about every gear change. Also, it has no lock up torque converter in 4th unlike most contemporary vehicles (and the VL!).
I have heard lots of complaints about the poor handling of VNs. Maybe the extra weight of the V8 over the front wheels helps, because at sane speeds the Calais is quite good to drive. It even turns into slow corners quite positively, unlike previous narrow bodied commodores that tended to understeer. However, as the speeds rise it starts to feel wobbly and unsettled.
Ride quality is OK, but a little rough for a heavyweight car with luxury pretentions. I think this has a lot to do with the solid rear axle - IRS equipped Commodores seem a lot better in this regard. Also, the car seems to bottom out on speed bumps - the extra weight of the V8 once again!
Can't complain about the accomodation - plenty of room with comfortable, if somewhat tacky, trim. Instrumentation is typical Holden plastic, but still better than previous Holdens I have owned. The trip computer is intuitive and useful, and the cruise control works well.
Having owned this car for less than a year, I can't comment a great deal on reliability. However, one of the positive things about Holden ownership is that if things do go wrong, parts are cheap as dirt and every mechanic and his dog seems comfortable working on them.