This is my first GL450 and my 2013 lease is coming to an end in 6 months and I am starting to think about the direction I want to go in. The number one annoyance I have deals with the defrosting of the windshield in snow or ice conditions. I cannot get the outside of the top one third of the windshield to defrost snow and ice no matter what I do. One time in Vermont, while it was snowing, I had to resort to using a hand warmer running back and forth on the inside glass while driving. I have everything turned to max and the cabin even becomes unbearably hot. It does help a bit to turn down the visor to capture warm air against the upper portion of the windshield. I have reported this to the dealer and even stopped at a dealer in R.I. during snowy weather and received a half hour tutorial on the operation of the climate system (learned nothing new). It has been checked by two dealers and proclaimed 'working fine'. This is the very last issue one would expect from a car company that cut it's teeth in the Bavarian Alps!
I have other issues with the car but none that are so frustrating and at times unsafe. I am exploring all the information I can get on the new Audi Q9 as well as trying to learn if the new GLS will be any different. It seems that you spend a lot of money to not be bothered by these issues.