It's the pistol that James Bond 007 would be carrying in real life, instead of the fullsized version. Tho the real live versions don't have the unlimited ammo capacity of the movie guns.
OldFart and UE have provided a lot of great, useful information.
So here's what I can chip in, as far as just from user experience of the p99c.
Not quite as ergonomic as your PPQ, especially with the only having the 2 finger grip frame. However, they come with a flat base and pinky base mags, and the pinky grip really does help. It does still fit really well to the hand, and it's really easy to grip quickly, on the fly. May not let you get the web of your hand up as high and tight to the gripframe as your PPQ, but it's still a great shooting grip position.
In double action, it's going to feel about the same, but with a slightly heavier pull than what you're used to with the PPQ. It's NOWHERE as heavy as a DA revolver, or most DA autoloaders. For DA, it's a really low pound feel, that is nice and smooth all the way back. Now, LIKE your PPQ, when you hit that break point, it's actually soft enough, that if you're pulling with enough strength, you'll miss it. Wont even feel it, just pulling the trigger back, and Bang. I'd sum it up by saying that the DA pull on a p99 is like having a strikerfire pull with a bit of extra weight for safety.
In SA mode, it takes a bit of getting used to. The trigger starts out all the way forward. You can take it back, about an inch or so, and it will stay there, what I call (probably incorrectly) stage 1. From Stage 1, its going to feel almost exactly like what you're used to with your PPQ. Reset may be a millimeter or so longer, but that's about it.
Also again, if you're easing that trigger back rather aggressively, it can be one smooth pull, miss the wall, and bang. Or if you're not being aggressive, it's one smooth pull, hit the wall, then bang.
Pointability- great. Comes up almost exactly where you would be pointing your finger, when you bring the barrel up.
Sights- plastic. 3 dot. Pretty much exactly what you're already used to with the Q.
Now, I can't remember if you own M1 or M2 PPQ, but the p99 uses the same paddle release levers as the M1.
Weight- honestly...these things feel LIGHT. Even fully loaded, they feel light. This is literally the first polymer pistol I've ever owned, that when empty, the balance felt like more weight was in the grip, than in the slide.
Putting one in a holster, and then on a belt, I can feel the pressure of it being there, and that's about it. It pretty much feels about like having a large cell phone clipped to your belt.
Appearance- Beauty is in the eye of the beholder, and the eye beholds beauty when you look at one of these pistols.
Shootability- (Now keep in mind that mine is 9mm, I haven't shot one in .40) For a gun this size, as a subcompact, overall really good. Walthers are a tad bit more flippy than my HKs, but it's nothing painful, stressful, or anything like that. Honestly, my old Beretta 92fs kinda hopped higher than one of these little guys does. And the double recoil spring in them does a really great job of handling that kick.
Compared to my HK VP9sk, which is a tad on the chubby side, the p99c is nice and flat. Not as thin as a single stack, but hey.
Overall impression- You won't be sorry if you buy a p99 or p99c. They're a gun that I think everybody should at least try out, and preferably own.
They're the choice of carry for a lot of people, and I probably would, if the trigger system on my VP9 hadn't spoiled me. And I say that cuz the VP9s trigger break is right there where Stage 1 is at. If I were carrying the p99c, I'd pull the trigger back, hit stage 1, and wonder why the thing didn't fire, if I was in a combat situation. But that's just me.