I love the old simplicity of OAD&D, and even more so of OD&D (the 1974-1976 rules). Skills, feats, kits, and what-have-you make everything a chore rather than a game. I don't want to spend a long time making a PC, and as a DM I don't want to have big stat blocks for my monsters and NPCs.
I don't like having a rule for everything. IMO, if it's not in the rules, the DM should make a judicious judgment of a proposed action's chance and roll the percentile dice. If a DM doesn't have enough common sense to do that, I wonder about his qualifications to be a DM. If a player won't abide by his DM's judgments, I wonder about the motives of that player. If a good player finds himself in a bad DM's game, no amount of rules is going to make that DM a good one; hence, he should find another DM.