I came up with this idea yesterday. I would really like some feedback, so if you would be so kind as to comment, I will greatly appreciate it.
I don't really like have a to-hit roll of 20 represent a critical hit. It essentially means everyone crits at the same rate. I don't like "confirming" crits, either. I've discussed this in an older post. I think the damage die should be the indicator, but I am against exploding damage dice.
OD&D is about modelling results. With that in mind, I had this idea. If a player rolls max damage, he gets a +1 to-hit on his next attack against that opponent. This represents such a severe flurry of blows that it affords a continuing advantage. Really it represents the potential to do it bring the fight to a swifter conclusion, thus modelling the result of critical success in combat. I also like it because it can only occur as the result of a successful hit, which means that characters and creatures with better to-hit numbers will achieve it more often. It is also a small bonus which is well in-line with the OD&D philosophy of such things.
Please let me know what you think.