Im not disappointed with who it is... i think he played it out very well, its just all the unanswered questions...
i guess the he is mar can be he is McA... 
but things like rosalind harker...kristina frye...the list. he said he had friends but who are they? connection with visualize...how stiles knew where Frye was...etc

i hope they do answer some of these questions because would be sad if they dont