There are really only three contenders: Gen 1 to Gen 2, Gen 2 to Gen 3, and Gen 4 to Gen 5.
The jump from 2D to 3D (Gen 4 to Gen 5) was probably the most substantial as it allowed developers to create entirely new kinds of games and experiences that weren't possible when games were limited to just two dimensions.
The jump from Gen 1 to Gen 2 was pretty substantial as well, as Gen 2 saw the first consoles with interchangeable cartridges, each with their own unique self-contained games. Gen 1 systems were essentially just Pong machines. Going from that to systems like the Atari VCS was a huge leap, at least in terms of what the hardware was capable of.
After that would be the jump from Gen 2 to Gen 3, mostly by merit of how much gameplay experiences evolved. With a handful of exceptions, Gen 2 games were very simple fare that was either ports of arcade games or otherwise tried to emulate the arcade experience at home. While titles based on arcade games still existed on the NES, there was a widespread proliferation of games, many of them original to the platform, that never really had an arcade analog, and some of them (especially RPGs and certain action-adventure titles) were not really suitable for the short-term nature of arcade gaming. During Gen 3, gaming quickly ceased to be defined purely by the kind of "rack up points to get a high score" fare that had defined the medium from Space Invaders on through the first half of the 1980s.
All other generations were merely extensions of the ones preceding them, reiterating on and refining established types of games, but not really bringing much of anything truly new to the table. They were evolutionary, not revolutionary.
Last edited by Shadow1980 - on 08 December 2020