...could I see Plan A, please?
That was - meh... People laughed at your Zombies when they were alone, and they looked even sillier in huge amounts due to lackluster CGI. I see how the putting the pieces together globally might have worked to create something special, but of course not in a Brad Pitt centric action movie. (PG13 rated, furthermore - if you cannot show a crowbar getting stuck in a Zombie head, don't make it a plot element).
So the only thing different from your run of the mill Zombie flick is the 3D (totally useless), the bright colors (that make your CGI Zombies oh so more obvious) and the global scenario - wasted by just having Pitt drop in an out and having the same Zombie fights in 4 different locations.
I give it 3 out of 5 brains (which those Zombies don't even want ;) )