My biggest complaint (fixed in later models) is the ability to lock your keys in your trunk if you approach a locked car, open the trunk, and accidentally drop in your gym bag or briefcase in and close it. Even though fob is just inside the trunk, it stays locked (no delay, no beep warning -- nothing).
Credit Buick for fixing, but never should have been an issue. This may sound strange, but if I'd had know this before buying, I might have thought twice. I'm at the gym every day, and always have to resist urge to plop keys in my bag with other personal belongings for fear I might drop bag back in trunk and have to call someone to come get me. Every buyer has small "pet peeves" that are a big deal for them in particular, and this is mine.
The other overriding issue is weight. The car is too heavy. It hurts handling, accelration, and fuel economy. There is no reason in 2012 that Buick can't build lighter cars that still offer quiet luxury.
Some of the symptoms addressed with newer, more powerful V-6, but still car needs to drop 400 pounds if Buick wants to continue to try and expand their age demographic downward.
I've learned to live with lack of storage, poorly designed armrest, no trunk release, ventilated seats that just lightly suck sweat off your body so only cool under very specific climate conditions, etc.
They don't bother me much anymore.