I would have been perfectly happy if Microsoft had just kept making the Natural 4000 forever. Logitech has some 20+ year old designs they keep producing because for some people they're perfection, and I'd hoped Microsoft would continue likewise since it's been well over a decade with the 4000 too. But nope, it's dead, and the replacement isn't nearly as good.
What don't you like about the replacement (nit the sculpt, the actual new design)? I consider it strictly better (namely because of the space bar being better).
2) Whatever the button on the left they threw between Ctrl and Windows destroys my mental memory constantly. I was hitting it all the time and never wanted it.
3) They moved Num Lock off the Numpad. Every time I need to find it I have to search because the new location is so counterintuitive and stupid.
4) Rather than one central location to check for the status of *lock, I have to look at keys scattered across the keyboard (including in non-intuitive locations such as "not on the num pad" for num lock)
5) They moved the Print Screen button to another place I'd never look for it.
I wasn't a fan of moving F6 to the left hand but would have gotten used to that eventually.
I had used the Ergo 4000 for 15+ years (and various older Microsoft ergos before that), but this made enough frustrating changes that caused me to look into alternatives out there. I ended up on the Kinesis Freestyle Edge. I didn't want to have to learn a radically different layout (Ergodox, Kinesis Advantage) and have to change every time I moved to a laptop or other machine, and the Freestyle gave me a mostly conventional layout, mechanical keys, and a physical split with enough tilt/tent to get to a very comfortable position.