Nothing special... Good way to almost ruin great horror franchise
First two movies are vastly superior. Why they chose to make a horror/comedy out of perfectly executed, tense, terrific horror franchise is unexplainable. Found footage style of filming worked amazingly well in REC and REC 2, it added amateurish and claustrofobic feel to it and the results were two near perfect horror movies. Choosing standard instead of handheld filming make REC 3 look like a bland mixture of Shaun of the Dead and Romero's zombie flicks (and many others that did similar things a lot better).
If you really need to see it then lower your expectations or at least try to watch it as a standalone movie simply called Genesis without any connections to REC movies. Even then, it's a pretty bland movie, polished but terribly mediocre, predictable and forgettable.