I had this thought in the Ascending AC thread. How do people feel about AD&D ability checks vs. WotC ability checks?
Just to summarize, in AD&D, the DM could call for an ability check, where you had to roll under your ability score on a d20. They could apply ad hoc modifiers, though I don't recall if there was any guidance for this- my DM occasionally asked for "roll under half" for very difficult rolls.
Non-Weapon Proficiencies were very similar, save that the base check was static, for example, making a Reading/Writing check, you had to roll under your Intelligence +1. Ad hoc modifiers could be applied to this as well. You could improve your chance of success by devoting additional proficiency slots (+1 per) but this was generally a terrible investment for PC's (especially once 2e exploded with the vast number of possible and occasionally overlapping NWP's).
Is the WotC system of d20+modifiers to reach a set DC better or worse, in your opinion? I think it's vastly better, but my AD&D DM naturally disagrees, lol.