As a Hitchcock fan, the premise of 78/52 really excited me. Like many cinephiles, I love Psycho...for its boldness, brilliant pacing and unforgettable performances.
One thing I enjoyed about 78/52 was the collective passion for the subject matter (the famous Psycho "shower scene"). The excitement from the filmmaker and interviewees was quite contagious; making the film very watchable from beginning to end.
I enjoyed the film's exploration of the shower scene's impact on cinema; specifically, its influence on Scorsese (and Raging Bull) as well as how the scene inspired an entire genre of subsequent 'slasher' films.
BUT...with that said, I struggled to find "new news". There is extensive research and discussion on Hitchcock and Psycho. A lot has already been explored. I found that 78/52 fell short of offering any fresh insight. Maybe it is because the documentary's interviews (mostly with with film editors) felt like a series of fanboys gushing over Hitchcock's brilliance. I found this to be quite tedious.
Lastly, I think the film needed to discuss Hitchcock's (unhealthy) relationship with women as an influence on his obsession with the shower scene. It is well-documented that Hitchcock subjected some of his actresses to forms of abuse (Tippi Hedren, Vera Miles). While Janet Leigh was always extremely professional/positive toward Hitchcock, I think the Psycho's shower scene desperately needs examination of Hitchcock, his own sexual obsessions with voyeurism and his general view of women.
If you're Hitchcock fan, I think you'll find 78/52 quite satisfying; even if it does fall a bit short of something new.