I have been shooting with the Leica SL and its dedicated Vario-Elmarit-SL 24-90mm lens since they were first delivered to customers on November 16, 2015. I've also used all of my Leica R prime lenses with it (fifteen lenses from 15mm to 250mm), all of my Leica M lenses (twelve lenses from 16mm to 135mm), as well as a smattering of other manufacturers' lenses. Leica has updated the firmware four times, adding features and amending behavior, based on both bug reports and user suggestions, with each update. I have had no problems with the camera or its lens whatsoever.
The Leica SL and SL24-90 lens has been extremely reliable. I've participated in discussions on four forums centered on the SL: reports of problems to date have been virtually nonexistent. Most of what little has been reported as a problem has either been a user misunderstanding how to use the camera or a feature that is missing. My camera and lenses have made over 10,000 exposures now and still feel, sound, and look as if new.
The SL's sensor has very good sensitivity. Here is a test shot at ISO 20,000, captured in RAW and processed at the Lightroom defaults with just a little cropping and the noise reduction raised from the default at 25 to 40:
Click on the image to see a full resolution JPEG.
I had a Sony A7 prior to the SL. The SL24-90mm lens out-performs any Sony lens I tried. The SL body unquestionably outperforms the Sony when used with any/all of my Leica M and R lenses, and particularly with the short focal lengths, and specifically when used with the same lenses. It has better ergonomics, a better viewfinder, and better build quality. The Leica shutter is in a totally different class compared to the Sony shutters.
I have had no difficulties communicating with Leica USA tech support, sales, or service personnel. Since I started using Leica gear, I have received nothing but excellent service for all my equipment—I've been using Leica equipment and doing business with Leica's US distributor since 1969, both as an amateur user and for my photographic business efforts. Whenever a problem has developed with any of the M, X, and R cameras I've owned, they've taken care of the problem quickly and efficiently. Of course, the SL has not yet developed any problems so I can't answer as to their service on this specific model.
The SL is my primary system camera now and works exactly the way I'd hoped a digital camera might someday work since I started using digital cameras in 2001-2002 or thereabouts. It is so competent and such a delight to use that I don't really see myself needing to replace or upgrade it for quite a few years to come. I've sold off several cameras so far (including the Sony A7) and will soon sell off my Nikon and Olympus kits as well ... they're no longer needed now that I have the SL.
G