While this episode is gratifying in that it indulges in Jane's obsession with Red John, a theme that has fallen by the wayside in the most recent season, it does little to progress the plot of the Red John - Jane Battle. Like in all the Red John episodes the only possible witness dies and no major evidence is left behind. I understand that the writers do not want to give too much away too soon, Red John will likely be a show long character, but by giving nothing away as to how the team will get closer to him the show feels static.
As far as personal development of the characters is concerned the plot of this episode simply confirms what had already been blatantly insinuated. The Libson - Bosco relationship was once romantic and that the Van Pelt and Rigsby's relationship is official.
While this episode may seem important by its inclusion of Red John and the exposure of secret relationships it puts nothing forward to progress the overall plot of the show.
What this episode does do however is provide an exciting 42 minutes of TV. Also the death of Bosco's team provides openings for future more interesting peripheral characters. Also with the death of three cops I expect that the way the CBI team views Red John will change. The capture of that particular serial killer will no longer be Jane's exclusive passion. I am curious to see how that pans out.