I can understand people not liking dickens (dont agree however) he does have a tendency to be verbose and use 20 words where maybe 2 will suffice (only part of this can be blamed on the magazine style publication). He is however a master of character development and is hilariously funny. One thing I have never understood is people disliking dickens and liking tolkien who rambles just as much if not more than dickens does.
Even if you do dislike him though, worst writer in the world is taking things to the extreme. As an example I detest reading Austen but I wouldnt call her the worst writer ever, I am sure it is relevant to some people (and therefore has merit making it impossible to be worst) just not to me.
I dont know about the worlds worst writer in general, but a scotsman named William McGonagall is generally considered to be the worlds worst poet.