I'm not gonna discuss Wrap here because it was already discussed on RBYk10, and I think they explained pretty much everything about the move, maximum power, minium power, avarage, and stuff, considering every factor possible (incluiding Golem and Rhydon!), except Gengar. So, yeah, no need to discuss that here.
Oh, yeah, about GSC's most important move, if we discard the moves of the first generation, I'm still insisting with Curse, just because you CAN'T find a team without a Curser, but you CAN find more than the 50% of times teams without Spikes, and even when we don't consider that, with a Spinner you can make Spikes pretty much useless, and the Spinners are pretty good, and even without that, as long you're able to force more switchs than your opponent, you're still having an edge, and more if you have some flyers on your side. As with Curse and other important moves of that generation, if you're totally unprepared for that, you're gonna have a bad time, but, yeah, that's the true for any important move, if you don't have any way to phaze, or stop a curser on its tracks, you losed.
Also, on RBY, Body Slam is on everything, you can't play a game without seen a Body Slammer over there, and it was a powerful, widespread, and with a nice paralyze rate move, and Normals get STAB from it. Softboiled is just on Chansey, and when Chansey is on every team, she's rarely the most powerful Pokémon of the game, and the same goes for the Recover users (but they really make things close).
Thunder Wave is just on Starmie/Slowbro, and when they both are great Pokémon and used a lot, Slowbro is still more used to abuse of Amnesia and Starmie to just annoy and clean with it's awesome speed and movepool.
But as game shapping move, Psychic is the most important move, without it, OU could be totally, but totally different, Psy dudes are not that strong with just Psybeam.
DDPt = Stealth Rock, by a huge amount, there is just no move that shapped so much a metagame as Stealth Rock, and while Rest on GSC was on almost everything and was the core of the metagame, it was still a move that you can deal with it, but Stealth Rock just shaped the 40% of the entire Pokéworld and is on literally any team, and all the teams, game planning, and literally everything, is planned around Stealth Rock. About an offensive move, Draco Meteor > Close Combat > U-Turn > Focus Blast > Any other stuff.