Watching this production I often felt that if the right lens or filter slid into place I'd swear this was an authentic episode from TOS' original run.
I've never had that feeling from any of the other fan productions. I can commend their efforts and admire their enthusiasm, but in the end there are often too many differences that distract me from getting swept up in it. It's much like feeling an author hasn't been effective at getting and holding your attention sufficiently for you to really care about his or her story.
This really did it for me.