Other than introducing new mechanics, I mean.
As you all may know, those games are placed upon some high pedestal for being considered the best. However, why is that?
What did the games do that the others didn't? Well, plenty, but hardly any of it was done well. I'd say most of it was done pretty horribly and that the generation as a whole is a pathetic pile of shit and that Gamefreak actually tried to push that as a fact on us with HeartGold and SoulSilver (better than the alternative, which is to say they were lazy and didn't feel like improving them).
So, back to the question, what did the games do right enough to put them in a respected position? My idea is simply their time of release being beneficial enough to get younger players when they were at that point where they'd accept any thing thrown at them regardless of quality so that in the future (which is present day) they could be all NOSTALGIA GOGGLES MAXIMUM ALL DAY ERRY DAY AWWWWWWW YEEEEAAAAAAAAAHHH. Any other thoughts?