I've been clear that the Reaction Roll is one of most valuable bits of Classic D&D. I'm not that fussed about how you resolve combat, tasks, character advancement etc., but I do think that having a simple means of freeing the DM from determining NPC reactions is something that every game could benefit from.
While browsing the other day I found this post, from late last year, by Alex Chalk of To Distant Lands, in which he breaks down the procedure for determining reactions into the Reaction Roll, a consideration of Interests, and modifiers for Disposition.
I need to get myself my own header. Well, in fact, my blogs need a total design overhaul.
Rather than repeat his work, you should check it out HERE. It is very likely to make it onto my GM summary sheets.