I downloaded exterminatus the other day, and its actually a lot of fun. It does need tweaking, though, there simply aren't enough ammo drops. Best to play it with mates so you can coordinate pick ups, some kids just run around the map hoovering up anything it sight.
"A widespread investigation of funeral homes, morgues, and hospitals has concluded that the unburied dead have been returning to life and seeking human victims. It's hard for us here to be reporting this to you, but it does seem to be a fact."