There is a difference in the quality of an H&K and that of other manufacturers. While most of the major manufacturers today (Glock, S&W, SA, etc.) make excellent products that are flat-out reliable and combat accurate, there is something special about an H&K that you can see and feel upon handling one. Once the first target is retrieved, the love affair is consummated. You may still love your other polymer pistols, but the H&K will be the most special.
The modularity (of the USP for instance) is incredible. The user can select a number of different trigger and safety combinations. With the addition of the P-Series, ergonomics are without compromise.
The fit and finish is second to none. Seriously. The other manufactures make great pistols, but they are NOT put together like an H&K; you simply will not see any gaps or generic fittments. Again, nothing against the other manufacture's design, but honest individual can say that H&K does not exceed the competition in this area. It is seen with the eyes and felt with the trigger finger.
The handling and balance are perfect. From the USP Expert down to the P2000SK, each pistol is well balanced and comes to aim without fail. They are a natural extension of the arm to most unbiased shooters. ...no "humps" or anything to get used to.
Reliability is military-grade. I have never, ever had a failure of any kind. I have personally run many thousands of rounds through the guns.
Accuracy? My USP Expert hangs with my Ed Brown and CCS Colts. It's ridiculous.
...yes, I am a fan. I speak no ill of (most of) the competition, but H&K has done a remarkable job of creating serious points-of-separation. Is it worth it? It depends on your taste and resources.