I absolutely love Daniel Linssen's works, and most of my all-time favourite games are patformers (Cave Story, Braid, FEZ, VVVVVV). Of course it's totally OK to create a platformer, but when there are so many awesome games of the same genre, it's not enough to make a decent game, you have to make a really good one, an interesting one, like Daniel does with his platformers.
The problem is not with the genre, for me personally, there is no problem at all. But if one wants to create a platformer, one must try really hard not to create "yet another platformer", since the underlying mechanics are so frequently used that it got pretty boring for a gamer to just jump around killing enemies while trying to follow a somewhat cohesive story.