As someone who played Everquest, nothing is more irritating than malicious players abusing collision detection.
IE, 10 Ogres block the doorway leading out of the plane of tranquility.... you can't pass it. Your character just has a running motion and can't move.

In Jeuno once in FFXI, we had something noted as the "great wall of jeuno" where literally hundreds of players blocked the narrow hallway from the stairs to the rest of the zone. It become near impossible to pass with so many players, that a GM had to come and scatter the players.

Collision detection is ok, but within reason. Realism takes a back seat to d-bags.