I saw the link and I am going to differ from everyone and say that they did an excellent job.  Here is why most dont like it, they spent years with their minds made up having publically declared their opinion.  

What they got so right about it wasnt on Red John but on Patrick. He has effectively been turned into his enemy now. Sure one could say his only victims are a particular serial killer and his accolytes, and if it stays that way many may not judge him for that.  But the darkness leaves its mark.  Go watch the first episode where Jane talks about true demonic evil, it is clear he has no idea what he is talking about however in now performing the sins of the one he hates he has in effect become like him in a small way, without the organization of minions.  

I just found the ending actually quite heartbreaking for Jane.  Only in a tv show would this ever work out as a good thing for someone.