IMO, the Nu52 is a big success.  I have been buying 36 titles (a step up over the old universe).  There are only a handful that I haven't enjoyed based solely on the merits of their multi-issue storytelling content. 

Specifically, there has been a major stride upward in quality and consistency in the 'core' character titles (Action, Batman, Flash, Green Lantern, Batman and Robin, Aquaman, Wonder Woman) and there are 'fringe' character books which are excellent (Swamp Thing, Animal Man, Batwoman, Frankenstein, I Vampire, All Star Western, Stormwatch).  And there are some books which are surprisingly, consistently entertaining (Supergirl, Birds of Prey, Legion of Superheroes, Demon Knights, Catwoman, Green Lantern Corps, Batman:  Dark Knight).

DC has got to view it as a success that they have elevated a healthy group of comics to where they are consistently outselling Marvel's top books ... previously they only accomplished that with event books.

The only downside, and its probably not really a downside, is that the 'new' world-explaining/world-building has come very slowly, particularly with characters like Flash, Superman and Wonder Woman where they significantly rejiggered their continuity.  Hey ... just tell good stories, and the answers will come in time.

Also coloring my overall favorable Nu52 impression is that I took it as the opportunity to go digital and that just makes the whole hobby more efficient, affordable and enjoyable for me.