I don't think there is actually anything wrong with the 370z but I see two problems with it. First is its the wrong car in the wrong place at the wrong time. The price of fuel, tax, recession, political green agenda, lack of money in everyone pocket has made people more cautious and sensible on how they spend their money. The second issue is the competition has been too tough, the likes of BMW, Audi, Porsche were producing cars which were faster, cheaper and more economical. Given the economical situation and this crazy obsession of being seen in an Audi, the 370z was certaining up against the ropes.
If none of the above affected you or bothered you, then as a car, the 370z is perfect. I know I would have one and will consider it at some point in the future.