I've had my Altima since 2005 and have put over 82,000 miles on it since then, and I'm proud to say it runs just as good now as the day I bought it. The 4-cyl engine has plenty of power, and the ride provides the perfect balance between comfort and sporty handling. I love how roomy the car is front and back, and all of the trunk space comes in handy. Some people complain about the growly engine but I kind of like it. The Altima is also excellent on gas, partly thanks to the 20 gallon fuel tank. The interior is comfortable and all of the materials are good quality. Mine has the convenience package which includes some nice features, especially the sporty 16'' alloy rims.
Styling, powerful 4cyl engine, fuel economy, comfort, overall reliability. Handling is great, providing good road feedback and being comfortable at the same time. You always feel like you're in total control of the car, even in the most inclement weather.
Some of the heat shields underneath will rust and need to be removed (they create an annoying rattle). This occurred at around 70000 miles. The wiggle-worm automatic shifter takes some getting used to.