The only things I have ever had wrong with this car, in the entire time that I have owned it, are things that I have done myself - i.e. accidents and such. The car is still in wonderful condition, even after all of this time. The only reason that I rated comfort a 7 is because the car is a tank and is relatively hard to park for new drivers. But other than that, the car is great. I am definitely thankful to have had this as my first car, despite how unattractive it may seem.
As of recently, the only problem I have is this belt that snapped off (I can't remember what it was called, I am sorry, but it made my steering wheel lock up and I had to pull over). My dad looked at it and it was just from the normal wear and tear - easily and cheaply replaced.
The only complaints I have about the car are it's handling and size. You have to slow down a lot for turns, so as long as you're not a speed demon then you're okay :)
The seats are very comfortable, the ride is always very smooth, and it is a very easy car to drive and maneuver.
If you are transitioning to a Buick Century from another car, the size may be hard to adjust to, but that really is the car's only downsize.
I haven't had to replace anything in the car except that belt, brake pads, and tires from normal wear and tear over the years. This car has been a very cheap car to maintain, and for that I am fortunate. I would highly recommend this car!
I am surprised the Century seems large to you, it was after all the smallest car in the Buick line-up. The Century is a very nice compromise between compact and full-size. I have driven several of the last generation Centuries (1997 - 2005) which were even a little bit larger than your car and I found them very easy to drive and maneuver. I drive a Park Avenue though, so I guess I am used to a larger car.