The upside: Smooth ride. Precise steering. Powerful acceleration (with the GL550). Fairly capable off road for a vehicle w/o locking differential. Prestige. Comfortable seat(s).
The downside: Maintenance cost(s)... E.g. had to replace all for air shocks (front about $1300--each; rear about $900 (for both)), starter motor ($800). Brakes actually last a long time and replacing rotors surprisingly "cheap" at about $350/axle. Tires only last about 20-25K miles (295/40-21) and there's a limited selection--a new set will set you back about $2200. The electronics were capricious--sometimes car wouldn't completely shut down when door opened (i.e. normal shut down is engine off & accessories stay on until door opened. started acting up sometimes where accessories wouldn't power down when door opened & had to open/shut door a few times to get it to shut down). Homelink garage door opener had a button that wouldn't work. EZ-GO door handles had to be replaced. Driver's side mirror folding mechanism broke. When I smelled leaking oil burning on the exhaust manifold, I knew it was time to get rid of it.
Bottom line: Surprisingly comfortable and agile for a 7 passenger, 3 ton SUV and most comfortable car/truck I've ever driven. However, after repair issues cited above, I'd be reluctant to own a M-B again.....
Update (5/2016): Traded in @ 120K miles. Reading through original review brought back bad memories of astronomical repair bills. There are better choices in the large luxury SUV segment.
I've got a 2009 GL450 with 65K miles.
My wife drives it for light suburban driving only.
In general, we like the vehicle, but it has been in the shop at least every three months.
We are now out of warranty and have had a flood of issues in the past month.
Three weeks ago the driver-side door lock mechanism went out.
The audio (radio, phone, everything) went out last week and the system needed to be reset.
This week, both front struts went out and nearly killed her (car was out of control).
The bill for the struts and the doorlock is $5K, but the dealer offered to pick-up some of the tab.
I've owned a lot of new mercedes, but won't buy another one.
Will never own a Mercedes again.
Non-stop money-pit from the day I bought it to the day I sold it.
Beware the air suspension on Mercedes-Benz.
Mine went "out" every six months or so.
Paint peeled off around the windows just when it was out of warranty.
I estimate I spent $6,000 a year in repairs.
It is also a huge gas guzzler.
I now have 94K on the vehicle and it is still great. I have done most of the work on the car since I like doing that and German cars are very straight forward to work on. I have only had to do brakes and oil and tires so far. Having an intermittent issue with the air suspension now, but will figure it out and fix it. The system is pretty simple and Arnott makes a good replacement for it that has very good reviews. Went to the Continentals for tires...a little stiffer, but so much quieter than the Perelli's. I've taken it on long trips, and into the mountains skiing in heavy snow. It handles everything quite well. They don't makes chains for the 20" wheels, but didn't need them.
This is my 2nd GL450. Hated the old one because of its many problems, but what can one expect when you are buying one of the first new models on the road. After driving an Odyssey for 2 years we decided to go for it again and I couldn't be more pleased. They have definitely improved a lot of things since 07. The ride is awesome, love the 20" rims, better nav, better rear DVDs, keyless go. I really love the running boards to help the kids get in on their own. Gas mileage ok, but what do you expect from a powerful SUV. This is a keeper.