For the most part, our ML has been very reliable. Regular wear and tear things such as brakes have been a bit of a hassle. We are constantly getting the handbrake adjusted as it just refuses to hold (I think this has been done about 4 times now).
Apart from that, the transmission - which Mercedes claim doesn't require servicing - has recently gotten a tiny bit harsh from 1st to 2nd under hard acceleration. Haven't had a chance to get it checked out, but it's really nothing major.
Another minor quirk is the brake dust on the front wheels, which is annoying, but a minor trade off because the EBD and the solid brake feel is just amazing.
The gauges seem to be a bit on the dim side. Not sure if that's just the way they are, but it's a very very minor issue.
Oh, and we've had one headlight blow (halogen).
Overall, it's been pretty reliable.
My local dealer (about 30 minutes away) is not the best though. Last time I went there for a routine service, I was given a Chevy Cobalt as a courtesy car, through their rental program. I was a bit annoyed that I was given this car, but the staff at the dealership are all courteous and very helpful.
For an SUV of its size, it handles quite well and is easy to park. It is a bit softer than the X5 my buddy has, but more firm and dialed-in than the Lexus. Feels almost car-like, and can be surprisingly agile.
AWD system is amazing, and the traction control system is phenomenal in the snow. Never tried with all assist disabled, but I'm sure that would be a lot of fun. Even with traction control off, it still cuts in occasionally. This would annoy me if I were driving a sports car, but since this is an SUV it's easy to live with.
The V6 has plenty of power, and is extremely smooth with the 7G-Tronic trans. Personally, in the future, I would go for a V8 but I think this V6 is also exceptional. It really shines on the freeway, with the 7 speed trans allowing it to hold the revs low and increase fuel mileage. Doesn't sound too bad either.
Interior is great. I love the wood trim and the feel of the seats. The seats are comfortable and give me a perfect driving position that feels comfy for miles on end. The heated seat option is amazing, with three settings and an automatic system that starts them off hot and then cools them down over time to bring them down to warm. No power lumbar support though.
The COMAND system is bearable, and the screen is great. Not a fan of the way the centre console is designed; there are gaps under the handles on each side of the console that iPods and phones slip through easily. Apart from that the seats, leather, trim and buttons are all very nice. The soft orange backlighting is also a great feature.
I think the looks aren't amazing (ours is silver with stock 17's). Even with the premium package in Canada, the grille is still plastic black and the rims are somewhat bland. Not as attractive as the new X5, in my opinion.
Haven't taken it for serious offroading, but the decent ground clearance and offroad mode would make it decent overall, I think. I've only given it some easy offroad stuff to deal with, and it was great. Wouldn't do any serious wheeling with it though.
Maintenance, as with all MB's, is a bit on the expensive side. However the services are completed in a timely manner and I haven't had to take it back to correct any errors made by mechanics.
At 55k kilometers, the truck is still fairly new and I haven't gotten a real sense of the reliability over time. Hopefully it will remain this reliable for years to come. My uncle had a well-maintained 2000 ML320 that he sold this year, and it ran like a dream.
Come time to sell it, I don't think I will get much. It's already depreciated to about half its value, which is horrendous.