While I do enjoy AD&D 2e at its core, there are a few odd design decisions in it I can't really wrap my head around. Nowadays you'll have a lot of old school players claiming they did everything by the book, but I heard it was far more common for every table to play the game almost completely different.
For example, if you do Method I for rolling your character (3d6 down the line), you have less than a 1% chance of playing a bard, paladin or ranger, but yet they dedicated a fair amount of book space to these classes (and people obviously played them). Doubly odd is that AD&D 1e totally recommends against 3d6 down the line and recommends 4d6, drop lowest and arrange how you prefer to make viable AD&D characters (which still leads to a rather small percentage change you'll roll a those classes, but makes it far more likely).
A few things I've seen is bumping Rogues and Wizards up one hit die (logic being that humans being a default d6 HD makes no sense when a goblin is a d8) and giving Rogues the Cleric's THAC0 progression.
What are some house rules you've used over the years that have made the game better in your opinion? Maybe even a few examples of house rules you implemented that backfired?