I bought my G3 in August of 2009. I currently have 71,100 miles. I have not had any mechanical problems, however I have 2 camshaft position sensors go bad. This causes the car to sputter and lose power and causes a lot of jerking which is bad for the transmission. The ride is a little rough, about what you would expect in a sub-compact. Power is a joke, 12 seconds to 60 MPH, and fuel economy could be better, and other cars in it's class (from the same year model) get better gas mileage and still have better performance. On-Star never worked from the start and the dealership gave me the run around about fixing it, so it never was, not that I would subscribe to a nonsense service anyway.
Power Windows pretty handy in a cheap car, CD/MP3 player and exception FM reception with static reduction. Can easily tune in FM stations 80+ miles away in clear stereo. Very good head lights, decent Air Conditioning, surprisingly good heater for a small engine. Seats are reasonably comfortable, even on longer drives, however we'll discuss comfort shortly. One of the few cars today that still have an ashtray and cigarette lighter, also has an extra 12V outlet between driver and passenger.
Better electronics. While the car is mechanically sound and proven reliable, some electronic/computer related issues have arisen (thankfully) during the warranty period. The factory stereo has 180 watts of power, however the 6 1/2" speakers cannot handle bass due to lack of cabinet volume which results in distortion, even at low volumes, I would recommend a small sub-woofer to improve sound quality, and it won't take much to do the trick. I'm 5'9" and my knee is right against the center console and becomes notably uncomfortable on long trips. I would suggest a engine that can deliver more torque at lower rpm's to give better performance at highway speeds.