As a former player of the Tekkit mod for Minecraft, the three-dimensionality is what I miss. As good as it is, Factorio is so disappointingly planar, despite the tools they give you to manage belt intersection and materiel transfer.
Satisfactory does not have this global grid. It does have very limited local grids, when you lay down foundations, but even these are less powerful than the grids on Minecraft/Factorio.
This makes every stage of logistical planning more difficult, which is both good and bad. Highly organized Satisfactory factories are, visually, more chaotic than highly organized Factorio factories. But, they can also be more satisfying to look at; from chaos emerges beauty, against all odds.
For me it's exactly the opposite. I very, very rarely enjoy a 3D game. Factorio's 2D world is a huge plus for me.
I'm definitely an outlier in this opinion, but for me the games industry took a seriously wrong turn in its embrace of 3D games, and I really appreciate it when I can find a solid 2D game like Factorio.
But, the world design is totally incredible; it begs you to explore every nook and cranny, and its non-random, so you can link up with friends and share secrets you've found. There's far more super-fun goodies to unlock, like the hypertubes or bounce pads.
Its just different, and I think someone who enjoys one would enjoy both. I tend to tell people to start with Factorio, though; its simple, yet infinitely deep. After about 50 hours in there, you'll gain a new respect for some of the simplified mechanics and fun-factor of Satisfactory; 50 hours there, and you'll gain a deeper respect for the nefarious complexity of Factorio. They complement each other perfectly.