The whole point of this episode was not to just reveal the identity of Red John. It was to explain every clue we had.
"He Is Mar", how did Red John guess the list of 7, the Visualize farm, how was he always one step ahead of Patrick, I expected A LOT of flashbacks, explonations for example what "created" Red John, Bosco's final words, Rosalind's description being different from the actual appearance of RJ, Kristina Frye's zombiness, and most of all I think - I wanted his reveal to be a thrilling second, no matter who it would be, I wanted the moment of his appearance on the screen to be something to remember, and yet we figured out who he is after seeing the promo... That's just wrong, it's almost unbelievable... We had fantastic season 3 finale, the original reveal of RJ's identity, we had great season 4 finale, the "game changing" season 5 finale, they all were supposed to lead to this episodes, those few scenes where it all was supposed to be explained. I don't really care who's Red John. McAllister is fine, I can live with that. But they explained nothing, even though choosing the character, that we saw only once in almost 6 seasons gave the writers a fantastic possibility to fit him into any Red John incident we've seen, so why wouldn't they do this? 
Also, I'm sorry, but if someone would tell me "yeah, the great Red John we know, the cold, sadistic, emotionless serial killer is gonna beg for his life like a little bitch, and is really kinda sorry for killing people", I would laugh this person to death...
That's really disappointing... I feel cheated... I always believed, that everything they did in this show will make sense after airing the episode like this, I thought that what they did wasn't just a random stuff they said and showed about Red John, at least in last 2-3 seasons, I thought it all lead to something. Turns out, they had no idea what they were doing... I'm not even angry, I'm just... yeah, I'm just disappointed.
Sorry for my english.