Actually, while I wrote “Wally” below, I think my biggest disappointment with the New 52 was that they didn’t go far enough.
They had a chance to completely reinvent the DC Universe to an extent that we haven’t seen since the dawn of the Silver Age. Instead, we have the same basic characters: Superman is still Clark Kent, Batman is still Bruce Wayne, Wonder Woman is still Diana, Flash is still Barry Allen, Green Lantern is still Hal Jordan (and John Stewart, and Kyle Rayner, and Guy Gardner), etc.
They could have tried to recapture the sheer creativity that made the Silver Age such a success. (What if instead of a guy with a magic ring, we make him a space cop? What if instead of a small guy who’s really strong, he actually shrinks to microscopic size?) Instead, they tried to recapture the success of the post-Crisis DCU. That’s still ambitious, but it has nowhere near the same level of potential, and I think that’s thrown a wet blanket over the past year.