Interesting... My mother has an Altima 3.5 SE and my dad has a G35 coupe, so I have a pretty good basis to compare.
I would have to say that the Altima is great for under 25k, but for more than that, the G35 is not even comparable. The fit and finish is significantly better and its a driver's car. The Altima, while a great daily driver, is a little too big and heavy for my tastes. Lots of mods available for either though...