I've own my 2014 M6 GC for about 2 years now. Prior to this, I had a 2013 BMW 528i and a 2002 Inifnit G20. The M6 is hands down, BMW's best looking car today. The interior is meticulously designed and very elegant. The full merino leather exudes luxury. The performance is superb. The car handles well and is very quick. Definitely a head turner.
As good as the car is, BMW is not very well known for it's reliability and the M6 is no exception. I only have 19K miles on the car and no major engine issues, but I've had minor issues. The car has lane departure warning and the steering wheel vibrates when you are out of your lane. I have had issues with this lane departure module on 2 separate occasions. It's as if something is loose in the steering wheel and every time you hit a minor bump over 55 mph, you hear it. Further, I've had minor issues with the electric seats adjustment not working properly as well as the headlight washers not retracting back properly. Not really that big of a deal, but if you take into account that this car is over $130,000, it becomes a big deal to you. I can say, however, that the engine has been fine. No issues whatsoever. But I am less then 20K miles. I'd like to hear someone with over 70K miles give a review on the engine reliability.
Overall, I am very happy with the car. There are tons of pros and minor cons with it. This is one unique car and one that you do not see on the road a lot.