It seems that everybody will be disappointed, whoever Red John is.
The fact is during the 5 past season, RJ has always been shown as the most clever, the most skillful, an uncatchable person almost divine always ahead everyone even Patrick Jane.
But, in the season 6, he appears to be "just" a serial-killer, he is beginning  to panic and make some (a lot) mistakes, he does not predict everything anymore.
With a face on his name, he appears to be vulnerable.

As everyone I always hope for a big twist, but in the same time, hurry to discover the truth....