Retro's games tend to receive wider acclaim so really it's quality vs quantity.
I don't know, I just looked up some scores for games from Retro and Rare and they're pretty much the same. Retro may be quality over quantity, but Rare was quality
and quantity. The non-Japanese thing is a good point, since Nintendo don't have very many of those... or maybe just Retro, I'm actually not sure. But I believe Retro is American and Rare were British, so they're still different.
Then again, I s'pose with Retro making a second Donkey Kong Country game, they're getting some more similarities with Rare in the kinds of games they make... although I heard these comparisons even before the first DKCR was shown. Metroid Prime doesn't seem like the kind of game Rare would make.