In terms of immediate impact, nothing comes close to the jump from 4th to 5th. Games like Ridge Racer for the PS1, Panzer Dragoon on the Saturn, and especially Mario 64 really proved what 3d gaming could do at launch and showed why the new systems were huge upgrades over the older systems.
5th to 6th also had a pretty big immediate impact. The Dreamcast launched with Sonic Adventure and Soul Caliber which were mind-blowing for the late 90s. The Xbox launched with Halo. And the Gamecube launched with Rogue Leader and very soon afterwards had Melee. The PS2 not so much though.
When it comes to the 7th gen I feel it took a while for the systems to show that kind of impact. The 360 was out for a year by the time Gears of War launched, the same for the PS3 with Uncharted, The launch games for both systems were not that impressive graphically. I kind of feel the same for the jump from the Atari 2600 to the NES. By the time the NES launched in America its games were a huge leap over the 2600, but when it launched as the Famicom in Japan in 1983 it didn't have revolutionary games like Super Mario Bros. yet.