I am for collision detection. Just because a game is a fantasy game, does not mean it can not have some sense of realism. With some games that have collision detection, if a pc or npc is blocking the way after a short period of trying to run through them you are actually allowed to do so. This would help prevent players from intentionally blocking passages. This feature would be turned off With mobs that are currently engaged, forcing you to actually run around the larger mobs to get to the desirable side and not through the mobs. The only problem would be with AoE healing/buffs spells. As it stands, conjurers do not have a really great AoE distance, their spells would need to be altered in order to supplement a party is surrounding a really large mob.