I tend to dislike most fancharacters because they tend to be un-original(See Sonic fancharacters that are recolors or female) or made just so the author/artist can sex up a canon character without Pedophilia/Zoophilia(sp)/etc.
But some can be alright, Zulu was a black and yellow fox Sonic character(I was seven or eight mind you) before turning him into a fully original character with his own story, family tree, set of characters, worlds, etc.
You know what the funny thing is? Catastrophix actually has his own story. I just stole him and modified him a little for the CoS.