I would hope it's generally thought that the series found it's high point in the DKC series. Sure, maybe Rare created DKC as a 'response' to one of Nintendo's competitors, but it's obvious a lot of love went into the creation of the three games as well. Gearing the series into a platformer, driven by a plot, and having created a non-Mario enemy in the Kremlings, they elevated the series out of becoming rehash after rehash of the original arcade series.
Then, after Rare's departure, the series was pulled in so many directions. Namco's Donkey Konga. The other bongo game by Nintendo of Japan, Jungle Beat. PAON's Jungle Climber and Barrel Blast games. And sprinkles of Mario vs DK in there.
If you pay attention, these games all portray DK differently, because people have different interpretations of what DK is supposed to be. There are those that believe that the DKC/R Donkey Kong is the same Donkey Kong that kidnapped Pauline in the original Donkey Kong games. And then there are people who believe that Donkey Kong is either the son(DK Jr) of the original ape (who is now Cranky Kong). I am inclined to agree with the latter and I think DKCR is a long-overdue return to form that was only kept barely alive with the PAON games.
Maybe this is a bad example, but imagine if the original "Mario Bros" (not Super) was the only Mario game that had been developed by Nintendo. And then here comes another company that ends up creating Peach, Bowser, Super Mushrooms, Goombas, et cetera. After three 'Super Mario Bros' games, 3 different developers each handle their own Mario projects; maybe one of them has Mario hitting bricks to pop music (complete with a weird drum peripheral that makes Mario jump), maybe two of them just have Mario and Luigi in a sewer, punching out crabs. No jumping on enemies. No mention of Peach or Bowser or Toad. Hey, maybe some people would like those games.
I think that's sort of how the DK series is fragmented.