They should definitely make another one, but there's two things that they should change if they do make another one..

1: Get rid of any and all motion controls. It's a 2D platformer... I should not have to shake the controller violently when attempting challenging and precise jumps just to execute a move (the forward barrel roll and ground pound) that could easily be mapped to another button. All we did back in the SNES days was push Y to roll forward... no ridiculous shaking of the controller necessary.

2: Cut down on the mine cart / forced scrolling levels. Yes these types of levels are staples of DKC games, but the reason for that is because there were only a handful of them in each of the originals. There wasn't an entire area devoted to nothing but mine cart levels or those annoying treadmill things that you have to constantly re-fuel to keep moving.

Take out these two things, and give us more original settings and level designs, and DKCR2 could be the best DKC yet.

I'd definitely like another Donkey Kong game by Retro. DKCR was - by quite a margin - my favourite 2D platformer.

That's fine. I'm just making the point that Retro hasn't given much of a chance to prove themselves yet.

I'm sorry, but I don't think Rayman Origins is more difficult. Though you may have a point, because after I beat DKCR, I somehow became very good at 2D platformers.

Donkey Kong by Retro is awesome.
(On a side note: like Metroid by Team Ninja is awesome. But only good people can appreciate it.)
If you don't like challenging games, that's a bad problem. Because challenge = reward. Especially when we're talking about a masterpiece like Donkey Kong Country Returns.
I would love for every game to be as challenging (and amazing) as Donkey Kong Country Returns is.
I'd take one Retro Donkey Kong every year.

They have not? I'd say working on 3 Metroid games and the DKC revival are very high profile opportunities. And they did well! But I wouldn't ever want to see them work on Mario or Zelda. I don't think Retro has the vision and innovative power of Nintendo of Japan's studios. On topic though, I have no problem with them making another DKC. I'm not sure if I'd buy it, but that's just me (bought DKCR and only played through it once, in a few days).

I mean that Retro cannot prove their ability to make an excellent Mario or Zelda game unless they actually make one. Now, Metroid and Donkey Kong have many similarities to Zelda and Mario, so I wouldn't doubt Retro's ability to make excellent action/adventure games or platformers. In fact, the first Metroid Prime alone is considered to be around the same level of quality as the best of Zelda, and DKCR is arguably better than Nintendo's recent 2D Mario efforts. From that point of view, how has Retro not proven itself as among Nintendo's finest? Whether or not they can pull of an excellent Zelda title will ultimately remain up in the air until Retro actually does make one, but given their track record, I will give them the benefit of the doubt.

I is a difficult game, but I've never been good at sidescroller platformers to begin with.

Donkey Kong Country Returns is one of the greatest 2D platformers I have ever played, and that's including the SNES DKC trilogy, Super Mario bros 3, Super Mario World, etc.

Retro's level design is genius, the way levels play out like a flowing symphony of gaps, platforms, enemies and hazards, and the way they tweak and mix simple concepts yo get far more variety out of them then seems possible.

It doesn't hurt that it looks gorgeous either, with incredible attention to detail (there's even tiny flies that give the enemy frogs a reason to jump on the spot) and a silky framerate, and while waggling to roll doesn't add anything, it didn't ruin it for me either. One thing I love that nobody else seems to mention is shaking the remote and nunchuk to pound the ground, barrels, and bosses was very satisfying, and added to the experience in a way that button mashing simply couldn't.

All this said, I don't want them to make another one right away because I'd rather they make something new, but I certainly wouldn't object to a DKCR2 for Wii U in, say, 2015.

"Arguably", "is considered" - what does that mean? It depends on who you ask. I liked NSMBWii much better than DKCR, and Metroid Prime is not for me. 

It was a smart move by Nintendo to establish a NoA developer, cause they are better at making certain types of games for western markets. Zelda and Mario are different beasts though. Previous experiments with outsourced Zelda games did not go well, the Capcom parts are the only ones I never finished. Felt like Capcom was given a LttP construction kit...

Why not leave Mario & Zelda in the hands of their creators? I mean, you don't want the next album of your favourite band to be recorded by another band either, right?