Jahydin
Hero
Anyone who loves AD&D and who really loves crunchy rules, Hackmaster is on Bundle of Holding on deep discount!
This game gets so much right... where to start? Maybe that anytime I see a post in the vein of, "I like D&D, but I don't like...", I almost always think to myself, "Hackmaster fixes that". Double dice for damage for a better average, high damage causing Threshold of Pain (ToP) checks that can drop opponents instantly (thus making big weapons and good CON stats important), the best initiative system ever devised, robust skill system... I can go on and on.
Which is probably why it's not as popular as its OSR contemporaries. With all that perfection comes a little bit of investment on the GM side. There is a lot going on. And although almost all of it is crunched before hand so play moves pretty quickly, I understand not everyone is as excited about reading the particulars of treating arrow wounds or doing the algebra necessary to calculate those ToPs mentioned above.
Even if it never sees play though, I highly recommend checking it out. I'm certain there will be at least a few rules you'll end up borrowing for your other games.