I've got a 2014 that I bought new, so it's pushing 5 years now, and I have a little over 50,000 miles on it. For the most part, it's been great. The highway fuel economy is fantastic.
My vehicle has not been without issues however. All 2014s were recalled to replace the catalytic converter (mine failed with the symptoms that triggered the recall - a check engine light, but no real change in behavior.) I have had other repairs done (the passenger side blend door in the HVAC broke a gear and had to be repaired, the rack and pinion was replaced due to leaking power steering fluid, and the front wheel bearings were replaced not long after I got the vehicle - all of this under the warranty and extended warranty I bought).
All that being said, aside from the catalytic converter which was recalled, I've had no issues with the vehicle due to the diesel engine or its fancy emissions system. Other people on this forum won't have that same experience however, and you'll hear more from people who had issues than those who haven't.
If you are buying used, I would inquire about the status of the class action lawsuit and how it impacts your purchase. For folks like me who have had their vehicles all along, we're getting an extended warranty for 10 years/120,000 miles total on almost everything related to the emissions system. You'll want to ask the dealership about that before you buy. I would assume it applies once the required software fix is installed on the vehicle, but you definitely should find that out.
Good luck! Any time I've thought about trading the Jeep in for something else, I drive it and then fall in love with it again.