Gamespot has obtained the Classification Board's report which cites excessive blood, dismemberment and decapitation as reasons behind the banning. The Board told Gamespot:
"When the player shoots an enemy combatant, a large volume of blood spray results and the enemy may be dismembered or decapitated. Injury detail is high with pieces of flesh seen flying from bodies when shot or a high level of wound detail visible on bodies. Post mortem damage occurs when bodies are shot resulting in blood spray, dismemberment and decapitation."
NecroVisioN currently carries a Metacritic score of 59/100.
UPDATE: Necrovision banned in Australia [Gamespot]