So prodded by the WOTC license fiasco, I started grabbing a few of the cheaper "OSR style" D&D type games. Basic Fantasy RPG, White Box, Dungeon Crawl Classics, and Shadowdark. At first it was just a fun rediscovery of the games I grew up on, and how well things like DCC & SD could adapt them to a modern version of the old school feel.
Now I'd come from the super long arc narrative style of the Pathfinder Adventure Paths that could span a full level 1-20 epic scale arc, with everything mapped out ahead of time. My first big shift came when running the AP Kingmaker, a sandbox style AP that still had a ton of railroad potential, but led to my players doing so many really fun and unanticipated things, growing whole character arcs by how they organically interacted with the world instead of planning ahead.
Then came the realization that open table games (sometimes combined with what is called a West Marches campaign) were absolutely ideal for busy adults with a mix of brand new kids and brand new empty nesters, with all the schedule chaos entailed by that. All of a sudden, I could manage to work in old friends from around the country with new friends excited to try their first RPG. Their characters could be as simple or deeply thought out as they were comfortable with, which was important with some new players that were at various points on the spectrum so certain types of role play would take a lot of time to really get into. It was also OK if some of them just wanted to stay a casual player because they enjoyed hanging around with the big RPers since they were always so fun to listen to.
Now I get a whole variety of game experiences each session I DM. Some players working out a deep purpose, or perhaps the trauma of their level 0 gauntlet (in many of these systems, players take 4 level 0 fragile new characters through a gauntlet dungeon, emerging with 1-2 surviving to take their 1st level, and with a backstory and motivations forged in that gauntlet). Some are devoted to building up philanthropy in their town, founding an organization, or spreading a faith. Others live to search forgotten ruins and dungeons. Another group loves the act of exploring the overland world to find the places that the forces of chaos had overtaken and bring them back into civilization. All these motivations lead to different but amazing styles of role play, and incredibly clever game play, and all that variety makes it a ton of fun to DM for.
And the best part is, the least prep I've ever had to do. At the end of each session, I usually have a good idea of what the groups next goal is, and I set to work making that next part of the adventure for them, with no time wasted designing things that players aren't ever going to be interested in enough to go interact with. All the things I spend time on get played, and that's really satisfying as a DM. Plus nothing beats being able to let all your friends be who they are, have fun how they do, and have some time to escape all the contentious topics and remember what it is to just be friends hanging out again, like we did in high school.