I purchased a 2011 E350 Bluetec with 80k miles. I did some research before purchasing and liked how the Diesel engines seem to take on lots of miles with out too many issues. I knew, however, that there were some issues and made a budget on how much I wanted to spend for the car and how much I expected to pay in the potential issues. That was probably the best thing I did. The Diesel engine for this year had two main issues that I came across in my initial search. The rear main main seal leaks as well as the seals or gasket on the oil cooler. Unfortunately for me, those were the first two things I had to replace... it was not unexpected but it would have been nice to have left the money in my bank account. The parts were relatively inexpensive but the labor cost was... well let's just say the mechanic I took it to was more than happy to do the work. I ended up spending about $2800 but that is far less than what it would have cost had I taken it to the MB dealership. That issue aside, the car is solid and drives extremely well. It's not a sports car but it is as fast as I need it to be. I drive primarily on the highway so 0 to 60 is not very important. I currently am averaging about 34 mpg. If highway traffic is light, I can get as much as 38 to 39 mpg. Heavy stop and go highway traffic and I am getting about 25 to 27 mpg. My work commute is over an hour so the time I leave from home or work does affect my mpg. Road noise is almost non existent... if traffic is light, I set the cruise control on 75 mph and just zone out to the road ahead. The day Mercedes sells an autonomous driving car will be the day I fall a sleep in the back seat. My wife drives a 2006 Lexus GX470 and it's not as quiet as the Mercedes. That being said, The interior is comfortable but it's not as comfortable as the Lexus GX470. I test drove the 2012 version of this car with the "real" leather seats and I could swear that the seats feel different (i.e. more comfortable) but I chose this one with the "fake" leather because of the price. The layout of the interior is good. My only issue is that the air condition controls feel too low in where it was positioned (a personal preference) and the cruise control seems out of place. I initially thought I would not like the position of the gear shift but after a while it did not bother me at all; I also thought that the knob in the center console would be annoying to use for the phone, radio, navigation but to the contrary I like it more than a touch screen. I really like this car and have been quite satisfied with almost all of it's features. It is not my first luxury car to own (it's my 4th) but is the first Mercedes I have owned. I will add, though, that maintenance is expensive. In fact, unless you can afford a good trustworthy mechanic, I would recommend you become a weekend technician. This means doing your own fluid changes (particularly the oil), minor engine repair and maintenance. My father is a retired Diesel mechanic so there is some advantage for me in owning this car but there are some things I just do not have the time for. Like the repairs I mentioned earlier. I left the car at the shop for 3 days on those two repairs. Funny thing is, I know how to do the job but I am not a certified technician that does stuff like that on a daily basis. If i can't do it myself over a weekend, then I have to go my mechanic... or I should say, my dad's friend who runs his own repair shop.
Update: 19Sep2017- Still love the car... but still am going with what I previously stated. It is not cheap to maintain. Even as a DIYer. I change the oil every 6,000 miles rather than 10,000 using full synthetic but after some research on the Mercedes Bluetec engines, I use 10w50 or 10w60 oil in the hotter seasons. 0w40 or 10w30 in the colder season. Texas is generally hot so I primarily use the heavier weight oil. I read a Mercedes technicians blog who indicated the engines run hotter than normal despite what the dealership may say. Using only the recommended oil at the recommended oil interval change may actually cause damage to the engine causing excessive build up of oil sludge. If it's under warranty... dealership will fix... but if there is no warranty, you either have a giant brick or you fix it yourself (or your very happy mechanic). Either way, preventative maintenance goes a long way.
Car still runs well. Stopped switching oil weights and have since stuck with the MB 229.52 recommended motor oils. The reason... soot really accumulated on the heavier oils. I replaced the EGR Valve because of it but in hindsight I may not have needed to. There is a cleaning process I go through on the intake and the DPF to avoid excessive soot and carbon. I do it before I change the oil. I’ve also installed an oil separator (oil catch can), which seems to work alright. I know it’s doing something cause I get better highway mpg (averaging 37 vs 34). Otherwise car runs well... I’m over 172,000 miles.