I've had a P320C 9mm for about six months. Hardly a torture test here...but I carry it almost every day and put 3000rds or so through it so far. Its held up and run flawlessly. Its as accurate in my hands as any other pistol I've owned, and much more so than my Glocks.
Major positives in my mind: 1) Trigger is the best I've ever felt on a striker-fired gun, with the exception of a PPQ. 2) Its incredibly simple in design. SIG could have easily dicked up the whole concept of a modular design, but I think they hit it out of the park here. The internals are all integrated into one stainless steel chassis that is much more rigid than a Glock or HK frame. No goofy tools or pins to mess with when taking in or out, but it fits securely in the frame nonetheless. The slide disassembles exactly like a Glock, which is a big positive for me since that's as simple as it gets.
Downsides in my mind: 1) Bore axis is significantly higher than a Glock or M&P. This matters more to some people than others. But if you're someone who's exclusively been using guns with a low bore axis, you'll need a little time getting used to this gun. 2) Parts/accessories availability. I'm hoping this is just because its a new gun, and production hasn't caught up yet. But if they're going to make this whole modular thing work, they better start getting the caliber and size exchange kits out there and available to the public. Right now Glock has the competition beat when it comes to parts and accessories availability, and SIG better get on this fast if they want to have a shot at taking some of the market share.
Bottom line: I think the jury will be out on the 320 series for another year or two, until it develops a track record with a major LE agency. But so far its pretty hard to find a negative review about it. I guess I've been one of the first guinea pigs this year and I'm happy with it. But there's no way to compare it to Glocks/M&Ps/etc. at this point.
Here's a video for those that like youtube torture tests:
https://www.youtube.com/watch?v=wU8-QHh2bR8