Not a massive fan of Vectra-C - quite a firm ride, which plays my back up a bit, but not uncomfortable (if you avoid the sporty ones). Its fine with smaller engines, but the more powerful ones show how horribly bad the setup is. I have frequently toyed with buying (a small engined) one though.
As MDTM says, its a million times better than the horrific Vectra-B.
Myself, if I wanted a large family boring car, I'd probably get (and it pains me to say this) the Mundaneo - I find it more comfortable, certain handles better, and the engines are mostly better.
The engines arn't, the diesels are woeful and sadly the petrols not much better.
They are a bit harsh on the ride but a much better chassis.....not as well screwed together though.
Its a subjective thing, but I reckon the tdci is smoother than the cdti, and certainly seems to pull better (imagine cars are similarish weight). The v6 petrol mondeo certainly lays its power down more gracefully than the v6 vectra. Not driven a small petrol engined mundaneo to comment, but i4 petrol vectras are pretty naff.
of the hire cars I've had, both mondeo and veccy-c have been robust. In fact, electrical issues aside, all modern fords seem robust - more so than (particularly) astra-h where trim keeps falling off.