PS2 to PS3. It's been diminishing returns ever since.

That one's that really blew my mind were super nes to n64 and ps1 to ps2.

I disagree ps4 was a massive leap to ps3.  Just compare red dead 2 to red dead 1 or spiderman ps3 to ps4 versions the leaps in that generation were pretty massive.

N64 to Gamecube

3D finally got viable and not just some blocky mess

NES to SNES for sure. There are barely any pre-SNES games I consider good.

While the introduction of 3d is ofc technically impressive SNES to N64 was honestly a sidestep imo, on average I'd say the games got worse but a few (OoT and MM) really outshined what had come before. Then the GameCube was another huge step forward where the average quality improved significantly.

The leaps for PlayStation consoles have been more gradual as I see it, but they've never felt insignificant either (perhaps not counting PS4 to PS5 which is too early to fully speak for).

Always the jump from 2D to 3D, so for this thread SNES to N64.

Imma gonna cheat because it's in the same generation as the N64 and it's only a 32-bit machine but the leap going from the PS1 to the GameCube is of a magnitude on a whole other scale.

Just look at the incredible shift from the original Resident Evil game from the original to the remake it had. The display in differences is still jaw dropping honestly.

3DS to Switch

It's tough to pick just one.
SNES to N64: This is a pretty obvious one, mostly in changing design philosophies for games that weren't possible on SNES.
Fifth Generation consoles to Sixth Generation consoles: Saturn to Dreamcast, PS1 to PS2, N64 to GameCube.
PS2 to PS3: The best-looking games on PS2 aren't close to The Last of Us.
Wii to Wii U is a pretty big leap, maybe one of Nintendo's biggest in specs for home consoles. The issue is that the Wii U processor was weak, and the architecture wasn't inviting. Unlike Switch where several games (at least) push the specs to their limit, I'm struggling to think of a game other than Xenoblade Chronicles X and its open world that truly showed the limit of Wii U performance.
3DS (even New 3DS) to Switch is a big leap, whether in handheld mode or docked.

I'm not really going to compare previous gens to mid-gen of their successors because that seems obvious. Going from an Xbox 360 to Xbox One X would be one of the biggest spec leaps in gaming history. Even a PS3 to PS4 Pro would be quite huge.

Technology wise, 2D to 3D (SNES > N64) is a leap we'll likely never come close to again.

While primitive 3D to competent 3D (PS1 > PS2) was the most impressive leap within that technology for me.

NES > SNES is in that category as well.
Also because controllers evolved from having only 2 face buttons to 6.