Red/Blue's sales? I doubt it. That was too much of an "event" and I don't think it'll ever be duplicated, much less surpassed. It's just that for a while there, Pokemon wasn't just a game - it was that generation's Hula Hoop.
I'd say though that Gold/Silver's critical acclaim was already surpassed by Crystal, and it could be argued that it's been surpassed at least a couple of times since then, already, with Emerald and B2W2. That illustrates the problem with "critical acclaim" though. Is it measured by sheer number of positive reactions or by the ratio of positive to negative? Do you only count "reputable" critics like metasites or do you count posters on message boards, even knowing that the 47 criticisms/compliments posted under 47 different accounts on a message board could still all come from one disturbed shut-in in a basement somewhere?
How would you rank the "acclaim" of RSE? The Hoenn games get a LOT of heat, particularly on /vp/, yet on pretty much every "favorite gen" or "favorite region" poll I see, they're no worse than third and often second or even first. So obviously a lot of people love those games, and the criticism they get is more notable for being loudly repeated than for being widespread. Or, similarly, look at the Unova games. For every poster who talks about how much they love the games/region/dex/etc., there's another poster who just goes, "RAARGH! ICECREAMCONETRASHBAGOVERDESIGNEDPIECEOFCRAPLINEARHAND-HOLDING!!!1!1"
So which counts more toward "acclaim?"
Personally, I'd say that G/S's critical acclaim has already been surpassed, and rightly so, and I certainly hope it'll be surpassed again, and repeatedly.
I could see an argument for Earth Power, at least with some of the Grasses. Being able to manipulate the ground seems reasonable for Grass types.
More broadly, I see lots of complaints about Grasses and calls for them to get better moves, but I don't particularly agree. Grass is my favorite type and I do just fine with them just the way they are. Yeah - they're a bit weak and their range of super effective attacks is a bit small, but I guess I just know how to use them since I like them and use them a lot. In any case, I just don't have much of a problem with them the way they are, and definitely don't believe that they need to be stronger in order to be useful. They're already useful if one knows how to use them.
I honestly think that what happens a lot of the time with things like this is that people get locked into one strategy - almost always fast, powerful sweeper - then they complain that the pokemon that can't do that one strategy successfully need to be changed since they "suck." It's not really that they suck though - it's just that they need to be used with a different strategy in order to make use of their potential. It's certainly not the pokemon's fault when a trainer doesn't know how to make use of them effectively. It's the trainer's fault.
Yeah - I was trying to figure that out. I had a memory of Natural Gift being a TM move, but then I thought it wasn't, then figured out that it's that it used to be but isn't any more. I'm not sure if they thought it was overpowered or if they just wanted to leave room for other stuff. It's only moderately powerful - generally 60 base power, or 80 with some of the more rare berries. But it does make for pretty much complete coverage, if only one type per fight (without Thief or Harvest or such).
Nature Power makes sense. Natural Gift too, I guess, though it seems it's not as directly connected to being Grass type, but more to being able to use berries effectively, though I could see an argument that Grass types would have an edge there too. Weather Ball I'm not so sure of though.
They should at least generally be able to learn them as TMs or egg moves or tutor moves or such - yeah. That'd make sense to me.