My mom has a 2004 Malibu Classic, purchased with 15,800 miles. It currently has 28,000 miles. It has the Ecotec engine.
It's been a great car. So far the only problem has been noisy strut mounts (for which a TSB was issued) and the selling dealer fixed (under warranty) not only the side that was making noise, but both sides.
The Ecotec has a cartridge filter, but I prefer it over a spin-on filter. It is accessible from the top, meaning that I can change the oil in this car without jacking it up. (Reaching the drain plug in any car, without jacking it up, is no problem for me).
I drove this car about 1500 miles last November (from DC to Chicago and back again), and it really is a smooth, comfortable car. Power-wise, passing was no problem, even on two-lane highways.