I too, have the Walthers in 9 mm and in 40 S&W. I bought the 40 because i liked so much the 9 mm. The recoil with the 9 is absolutely controllable allowing very fast and accurate rapid fire. Double action is not very long, and with little practice you can handle it. Also, there is the possibility of carry the pistol with the trigger foward in single action. Also, you have to practice with this kind of trigger because is something really unusual, and the death travel is a little difficult.
The 40 is a really different matter. Recoil is and entirely different matter. For me, is sharper than anyother 40 in the market. I finally sold my 40, and the next week the guy who bought it experience a ka-boom with it. It seems that the development of the P-99 was only based in the 9 mm, so the 40 perhaps lack the neccesary strenght. Even the slide and barrell of the Smith is a little heavier than the Walther.
In sum i loved the 9 mm.
On little more thing, i experience, after shooting with other models, that mi trigger finger have to get accustom again(excuse mi word) because of the trigger guard.