I agree that Donkey Kong is terrible on the 2600. Mario is pretty good (relative to SMB). Anyway, I don't disagree with you that NES is when we started to see faces (though they were still not very good). But, the fact remains that those characters were created and appeared on systems prior to gen 3. The fact that they made the generational leap, and Mario was spun off into his own series, is evidence that they were already "memorable characters", at least to some degree, before appearing on the NES. Definitely Pacman was memorable prior to the NES.
The Donkey Kong character really sucks on the 2600 though. Like, bigtime. Could be the worst looking character in the history of gaming.
I don't even consider arcades to be part of the generation system, but if you do, that actually highlights another reason why their was a big transition from Gen 2 to Gen 3. The best games transitioned from the arcade to the home. There were memorable characters before the NES, like Pac Man, but they didn't start on consoles. One big transition that happened with the NES is that home consoles started being considered the main platform. Before that the arcades were the main platform. This is yet another reason why Generation 3 was such a huge transition.