A club-mate and I were chatting after club tonight, and felt the (optional) critical hit rule isn't right for us, and we spit-balled a house-rule we were going to suggest to the club.
Got home to find that Jamwarrior had started a list of optional rules we were/weren't going to use, and had suggested the same house rule that my club-mate had been discussing.
Critical Hit: Any natural roll of a 20 will automatically hit the opponent, even if their modified roll is higher. If both players roll a natural 20, then the highest modified roll wins as normal.
Any issues anyone can see? Of course, this hasn't been tested yet!