It would probably be PS1 to PS2 or N64 to GCN.
Even if a lot of the models have looked crude for a while, it's the first generation where cartoony and realistic models look like people in 3D. The tech wasn't really there, especially for more realistic games before Dreamcast.
Switch to Switch 2 is a huge leap, Wii to Wii U was a huge leap.
The sixth generation was the first generation where 3D sandboxes and open-world became probable, though they were uncommon. Games that took 2-4 discs on PS1 were now succeeded by games that could fit on a disc. Shoot, there were even 2 PS1 games that had 5 discs. Even GameCube miniDVDs (including the few 2 disc releases) could hold so much more than N64 cartridges.
Lifetime Sales Predictions
Switch: 161 million (was 73 million, then 96 million, then 113 million, then 125 million, then 144 million, then 151 million, then 156 million)
PS5: 122 million (was 105 million, then 115 million) Xbox Series X/S: 38 million (was 60 million, then 67 million, then 57 million. then 48 million. then 40 million)
Switch 2: 120 million (was 116 million)
PS4: 120 mil (was 100 then 130 million, then 122 million) Xbox One: 51 mil (was 50 then 55 mil)
3DS: 75.5 mil (was 73, then 77 million)
"Let go your earthly tether, enter the void, empty and become wind." - Guru Laghima
