https://www.ableton.com/en/products/controllers/apc40mkii/tr...
https://www.native-instruments.com/en/products/komplete/keyb...
1. The entire page hierarchy was only one level deep. You had 10 buttons that select a parameter, and a single data entry slider. So, with two hands, you could very rapidly manipulate parameters. I believe the Yamaha DX7 also had this, but what made the ESQ-1 cool was that the button usages were listed right on the digital readout next to the buttons themselves, rather than off to the side and hard-coded to the parameter. So it was like hitting a hardware button that could automatically remap.
2. Again unlike the DX7, there was no button-press needed to "edit" -- you just hit the button and moved the slider. It felt very natural to use even though it was technically a digital parameter being editing. If you needed additional editing power, you could still hunt for the other buttons outside of the 10 "screen" buttons.
I had one about 5 years ago, and swapped it for a JP-8000. I regret it. Very cool synth, very innovative UX.