Traded in my 2014 GL 450 for the 2017 GLS 550. The GL was the best SUV that I have owned (Range Rover, Navigator, Yukon Denali XL). On the surface the GLS seemed to be very similar, but I have found it to be more comfortable with an even better ride. The seat comfort (in the front) is a step up from the GL. Operating this SUV is a pleasurable experience akin to driving a large automobile. I don't need the third row seats as often as I did (kids are grown), but the rear space is fantastic. I especially like the lockable under floor storage in the rear. The programmable driving modes are a nice feature as is the steering assistant. I also got the off-road package this time with the extra height adjustment and the low-range feature. This gives you some undercarriage protection and low-end torque that the standard 4 matic does not have. The 550 has quite a bit more power than the 450 did. The 9 speed automatic transmission is very smooth. The technology is great however, the ECO engine cutoff is automatically activated even time you start the vehicle, or when changing the driving mode. If you dislike this feature, you have to remember to manually de-activate it every time you start up. The interior has been upgraded a bit, but still needs to be more like the S-Class. Although the new center screen is bright and easy to read. GL's was a bit small. It is more at home on the highway than my Range Rover was and more comfortable. It's too early to tell about the reliability yet, but my previous GL was outstanding in that department. With the cost at around $100k, the GLS 450 is probably a better value. The 550 represents about $20k worth of extra horsepower, leather seating and bells & whistles. If I still had kids to haul around, I would have gotten another 450.
I have been driving the new GLS 450 for 2 months. I used to drive a Cadillac CTS and this new Truck gives me a similar driving experience (except that I don't want to do a quick/sharp turn) and sometimes it even gives me even more confidence in handling. It is very spacious; I keeps the 3rd row folded during most of time and carried lots of stuff in the truck (e.g. two large palm trees!). The interior is also very good for the price. The only major downside is the information system: if I had it 10 years ago I would probably have liked it lot, but in the year of 2016, this system is way too old fashioned. The information does not even have a TOUCH SCREEN! Instead, it uses a gigantic control knob with technology already invented in the 90's. Furthermore, some of the common controls are hard to find (e.g. turning on/off bluetooth) - one should be able to push a button to do it. If you connect your phone to the car via bluetooth, it can be very very annoying, so does the AirPlay feature, because the car will stop the music for any notification coming from your phone. And only two USB ports? Overall, I still like to drive this car without its old-fashioned information system, but I hope Mercedes can improve it in the next model - after all, if I could just replace that screen with my iPad, it would give me a much better information system already.