I own an early production KP90DC (stainless, decocker-only).
I originally had to have the slide replaced under warranty because of what I was told was a galling problem reportedly caused by a hardening issue. Nice warranty service, though. Typical of the Ruger folks.
I shot it quite a lot over the years and I've only had to replace a small number of parts on it due to wear and tear (extractor, firing pin, recoil springs, guide rod, magazine catch).
Ruger increased the weight rating of the recoil spring at one point (originally the 9mm & .45 ACP models used the same recoil spring). I was told by someone at Ruger that they did this because of some owners wanting to use a lot of +P in their guns. They also switched from the original 7-rd P90 to the 8-rd P97 magazines.
I carried my P90 as an off-duty weapon for a long time.
Reliable, robust, chunky, bulky, reasonably lightweight and sufficiently accurate.
I still use it at the range from time to time, but I can't remember the last time I actually carried it. I have range of holsters for it, including the previously mentioned Summer Special, a Don Hume H726 (my favorite), another open-top Hume holster (can't remember the model number) and even a plastic 'range holster' for bad weather. Probably a couple others in one of my holster boxes which slips my mind at the moment.
I think the Ruger could have better sights, but I've just never gotten around to replacing the 3-dot factory sights since it's always given me satisfactory practical accuracy under whatever conditions I've used it. Night sights might be nice, though. If I were going to return to carrying it that's probably a modification I'd consider.
Good durable, robust, reliable .45 pistol. Did I mention chunky?
How about 'hand-filling'?
The rubber Hogue wraparound grips are nice additions, if the finger grooves fit your hands.
Like the with the Sig pistols, the P90 grip screws seem to like to loosen themselves for sport.
This would've been a great pistol platform for the 10mm cartridge, which is supposedly what it was originally designed for during development, only being chambered to the .45 ACP when the 10mm appeared as though it was going to quickly fade from the LE/defensive market.
I have no plans to get rid of mine.