These cars have very serious powertrain problems. The pre-cat disintegrating over time and the bits and pieces being sucked into the engine, possibly causing engine damage, and causing oil burn. All 02-06 Altimas suffer from the same serious design flaw. For that alone you should avoid this car.
Other common problems include butterfly valve screws being sucked into the engine and causing damage, timing chain problems, floor boards rusting through, and rough-shifting transmissions.
Despite what the Edmunds review says the car is NOT fun to drive. The powertrain is extremely unrefined and noisy. It also only gets around 20 mpg in the city, which is pathetic for a 4 cylinder.
Styling, is probably the only attractive feature of the car, and the size, if you like large cars. Whenever I drive the car I feel like Nissan tried to make the largest possible car for the least amount of money. All this does not matter of course if the engine decides to self-destruct.
I didn't run into the dreaded pre-cat problem yet, but I've had to deal with a whole bunch of other issues. I've spent around $5000 in one year servicing this car (in independent shops). I bought it used, but I've owned other used cars, and compared to say the Toyota Camry the build quality of the Altima is a joke.