Having been an owner for just over nine months, as you are probably aware from my previous posts etc, a Ghibli diesel. I can confirm no major issues.
The stop/ start feature seems to activate itself on odd occasions, easy to disable again. The voice activation can be a little temperamental, particularly address entry for the Sat Nav.
Really apart from these, the reliability has been fine. I can leave the car 7-8 weeks at a time always starts first time. From what I have read on the U.S Ghibli forum, the diesel is more reliable than the petrol.
A lot of improvements were made for the 16my to improve reliability and refinement. and although at idle particularly from cold you can tell its a diesel if you listen listen to the engine, on the move it's probably quiter than the petrol, and a press of the sport button produces a V8 rumble allbeit digitally produced, from the exhausts.
Performance is more than adequate for me with 600 n.m of torque.
Finally although a 'diesel' Maserati, for me it has a specialness that's missing in the usual German competition.