I hate it, and my group does too. It completely flattens any input from having a good main casting stat, and really destroys the kind of flexibiliy the older system had. In the old system, a 4th level Wizard with 18 INT can prepare 8 spells. They can choose to prepare four 1st and four 2nd-level spells, or 2 1st-level and 6 2nd-level spells or anything inbetween. This allows them to be a lot better prepared depending on the situation.
Under OneD&D's new system, every 4th-level Wizard can only prepare 4 1st-level and 3 2nd-level spells, no exceptions. Not only did the full casters lose the flexibility about which spell levels to prioritize (our party's wizard only prepare 3 1st-level spells and saves the rest on more important, higher-level spell selection for instance), but they're no longer rewarded for prioritising raising Intelligence either.
I can see how the old system felt complicated, but having taught the game to 10+ new people, they usually caught on if you gave people a little time, and most of the time an analogy of "Each spell you prepare is like a gun you choose, and the spell slots are the bullets you can use for your guns" was sufficient. I feel like this is pointless simplicity.