I've had this car for 9 years now- it's been great. No major issues,a few flaws, but 1998 was the first year of the new model. I have about 210,000 km (divide that by 1.6 for miles) and I just did regular maintenance. Very confortable and quiet. As it is getting older, I consider replacing it with an Audi A8 or BMW 760i but in all honesty I have no reason other than getting a new and fancy toy. I highly recommend it (check the J.D. Power reports on Buick, both Century and Regal).
Smooth ride, quietness (it happened to me several times when I tried to start the engine when the engine was actually running), reliability.
GM should have kept the engineering and changed the exterior sheet-metal only. Cup holder ingenious but flimsy, to honk you have to press hard and I find it being a safety issue, rubber seal sticks to the windows.