I own three. Of all the pistols I own, and I have more than a few, the P99 AS are the ones I shoot the best, and the ones I count on if things go bump in the night. I have installed Trijicon night sights on all of them, an easy job with the P99.
If you start hunting for mags, do remember that the PPQ M1 mags are totally compatible with the P99 series. M2 mags are not.
I have picked up a couple of the 17 round PPQ M1 mags, worth it if you want to up the round count a bit. Also, mags for the Magnum Research MR9 are the same as P99 mags. The MR9's frame was actually made by Walther.
The single action stage of the P99 has the same (some say better) break and reset as the much ballyhooed trigger of the PPQ. The reset is ultra short and fast, so just be aware. Once you master it you can attain an outstanding rate of fire.
If my HK45 had a trigger as good as the P99's, it would be the perfect 45.