I'm not fussed about it being DK but the fact it took over 3 years to make a sequel to a platformer (yeah I know, it's HD and has 3D camera angles) was what disappointed me. Should have been a launch game and their next game should've been nearly out by now.
The problem was Retro Studios didn't have enough time to do a launch title for Wii U, not when they just released DKC: Returns in November 2010, then they needed some time to adapt to HD development too. By early March 2011, one of Nintendo's producers, Kensuke Tanabe, stated there were no "current plans" to do a sequel to DKC, so Retro had not yet even decided on its next project at that point. From what we know, DKC: Returns started development in April 2008, 8 months after the release of Metroid Prime 3, it took around 2 years and 8 months to develop DKC: Returns. Of course, we also know Retro needed to hire more staff to compensate for HD development after they had some staff leave right before DKC: Returns started development. It shouldn 't have impacted development much, but Retro also moved into a bigger office building by Fall 2012.
That comment from Tanabe is basically what made us think they weren't going to do a sequel despite the game having sold 4.9 million copies the same month his comment was released. Of course, Tanabe admitted Metroid Prime wasn't initially conceived to be a trilogy until the end of the first game's development, so they ended up doing something similiar in their decision to do a DKC sequel.