@critfail_press #CastlesAndCrusades and #ADnD2e for sure. I love C&C for the simplicity of the SIEGE engine mechanic from what little I've gotten to run with it. AD&D 2e was the first game I played and I love it despite/because of the weird sub-systems for rolling. I'm going to run an Al-Qadim based backup game for my Pathfinder group.
I've even started running my Pathfinder game more OSR-style. My players are incredibly creative and I find that I need to make a quick, fair ruling on the spot if I don't want to drag things down looking for specific rules. A couple of my players do usually have tablets or computers up to help me find some rules on the fly though, so that helps.
I find that there's an incredible amount of trust required for OSR games. You have to feel like the GM is going to be fair and balance resolutions for the story and for the characters. I think it's a little more intimate of an experience, which I love. I feel honored that my players trust me to bring a satisfying gaming experience at my table and I don't want to betray that. It makes me be a better GM, I think.