One category of movie that should never be average is the zombie flick. Better wickedly good or delightfully bad, but not average.
World War Z is decidedly average. It never gives the sense of epic catastrophe that the zombie epidemic in its premise is made out to be, nor does it offer the smaller-scale scenes of tension that I Am Legend accomplished so well. And just as the film begins to pick up with a couple of impressive action set pieces, it promptly falls apart with a strange change in tone, painfully simplistic storytelling and the most anticlimactic of anticlimactic endings. (It was widely reported that the studio spent huge amounts of money to re-shoot the third act. Good to see that money was well spent.)
For cheap zombie thrills you could do worse but you could also do better, starting in the B movie section.