Not an owner, but as an observer. So far to date, except for a few early build issues that were largely resolved in 2012, it seems like the motor is a good critical success for Ford for the most part. In 2015, there were added features to the 6.7, aside from horsepower and torque, the engine gained an exhaust brake which makes it much better for towing if you cross grades fairly often in your travels. The pre 2015 trucks do not have much grade braking. The only common issue I've seen out there is a problem with leaking radiators that occurs often enough. However, the aftermarket has already stepped up with Mishimoto radiators should you lose yours.
As with all modern diesels, it is critical to stay on-top in regards to maintenance. Do not defer anything, especially fuel filters.
Also figure that it'd probably help to explain the modern emissions systems of diesels in further detail. New emissions have a particulate filter and Oxidizer catalysts (that uses diesel exhaust fluid aka DEF) in the exhaust stream. Regeneration is really only for the particulate filter. This is when the engine enriches the exhaust flow with more fuel (either through post-injection which Ford and RAM utilizes, or an extra fuel injector in the exhaust stream which is what GM does with 2011+ trucks) to raise the temperature. This higher temperature ignites the soot built up in the DPF and turns it into a fine ash that escapes out the tail pipe. Driving hard and putting a load on the engine actually helps regeneration by raising the temperatures without additional fuel. This in turn means a "Passive" regeneration which requires no additional fuel and burns off the soot buildup naturally. So if you're in regeneration, it's actually best to maintain a steady state load on the engine for about half an hour to an hour to burn off the soot. Diesel exhaust fluid is only used for the oxidizer catalyst to get rid of NOx in the emissions and break it down into nitrogen and oxygen.
Here's a pic to help illustrate the exhaust flow:
And a final pro-tip. I like to get my DEF at truck stops. They turn over DEF pretty quickly and that pretty much ensures a fresh supply. If you get just DEF alone, you don't have to go through the song and dance of giving them your license plate and all that other info since it isn't taxed like fuel. I only pay 2.79 a gallon for DEF and I re-fill a couple 2.5 gallon DEF jugs and keep them on the shelf to top off so that I only make the trip once a year to buy DEF. DEF also has a limited shelf life depending on average temperatures and how long it's been exposed to it.
