My girlfriend has a 03 sunfire with the ecotec motor.
The interior is absolute garbage, no room at all in that thing (hers is a coupe).
The motor is great, very reliable car.
As for problems, they had a lot of problems with the headlights in that thing. They put some pretty complex headlights in that car (dual bulb, plus fogs), instead of a 9007 or whatever headlamp. Fluid from the washer fluid tank would leak into the harness and short it out. There is a recall on the work, but the dealer that did the recall on her car did a total hack job, and the problem with dimming headlights came back. We had to rewire the entire headlight system from the switch all the way down… After it was wired right, and the leak in the washer fluid was corrected it has been no problem.
Also the rear drum brakes like to lock up, no matter what you replace on them. They squeek and sometimes grind. Its the third sunfire I have driven with the problem, so it isn’t an isolated issue.
Other than that they are cheap cars to buy. The insurance on the coupe is more than most economy cars because it has a bad crash rating.
We paid 4500 for hers with 39k miles on it.