The H&K Mk23 as well as the USP and HK45 are just incredible pistols. H&K just hit a home run with these designs.
On more than a few occasions, I've had folks comment on my H&K USP45 Elite, asking me what it is, then being shocked that it's such an old design because they thought that it was something brand new by the look of it, which to me indicates just how far ahead of its time the design really was that folks mistake it for a modern pistol.
I don't blame them either, because let's face it, it does have a sort of futuristic look to it. In fact, when I first saw this USP Elite, I myself thought that it was a whole new gun, despite the fact that I was aware of the USP, because the streamlined look of it does indeed make it look like another gun.
However, I must admit that part of my attraction to it was that it sort of reminds me of the Walther PP, like some modern variation of it. So I guess it's sort of retro-futuristic-looking to be precise.
To me, the absolute coolest part about the Mk23 and USP45 is that they can handle .45 Super/.450 SMC right out of the box. I don't believe that there are any other pistols in current production that can take .45 Super without modifications.