Ergonomics are solid. The P320 fits as well in my hand as my M&P 9C, or the H&K VP9, or the Walther PPQ. I find it a bit more comfortable than the XDM series. I say solid and not great, as the slide height/bore axis is higher than my trusty M&P and the grip angle is different. I can draw my M&P and get right on target; that's not the case with the Sig. Of course, that's also because my M&P is the one I train with the most and carry the most.
Speaking of sights, they are SIGLITE® Night Sights and are quite good, especially for stock sights. Big enough to pick out, narrow enough to see light around the front sight. I read on the Interwebs that you have to hold at 6 o'clock at 10-15 yards. I found that holding on the desired POI worked at that range for me.
Right now, still debating selling it or keeping it. I want to like it, and I do like 9mm carry guns. Maybe some more time on the trigger to see how rapidly I can get accustomed to the different grip.

(1) I know, I know. But I bought a SP101, and I hate having safe queens.
(2) The new M&Ps have better triggers, like the M&P Shield. I also read that Smith and Wesson is dropping the Pro Center triggers across the whole M&P line.
http://mindflayer.net/2015/04/16/sig-sa ... ge-report/