Nothing.
Overall, my wife and I have no complaints. The interior is a bit smaller than we would like, but we can't afford a bigger car at this time. Don't like the fact that the doors don't lock automatically after you get in. I was a little nervous about buying a Hyundai, but since our previous Buick was a piece of crap I was ready to try just about anything.
I also went from American to a Hyundai Sonata. My father works for GM so there were troubled times when I bought the car. However, after about 2 months he drove the car and commented on how quiet and nice it is. "better than a Malibu" He said (and less expensive). After 54,000 miles on my 04 LX, We have had 0 problems. I will look to Hyundai first for my next car.
I just purchased an 04 Sonata GLS. I love it. It's a very quiet ride, easy to handle, sharp looking too. I get a lot of comments of people thinking it's a Mercedes or a new Lincoln.
My car only had 30,000 miles on it and had never been scratched, dented, smoked in. Tip top shape.
Theres nothing more I could want from a car that this one doesn't have. The trunk is roomy, the seats accommodate individual drinks, the cd player and tape player are easy to use. The gas mileage?? well, for a 6 cyl its not too shabby. The car has some real get up and go to it. I would definitely buy another Hyundai product. I too have GM family members that gave me some problems about my purchase, but in the end, I'm the most satisfied customer of this quality made car.