Delver is the thing I was looking for to get people who only ever played D&D a thing that was familiar enough to them to try without reservation, but that got them instantly into a completely different mode of play than they'd ever tried before. Collectively building spaces in the dungeon makes players feel more invested in exploration, and leads to some truly surreal and unique journeys. Everyone is given the opportunity to push for the kinds of challenges, set pieces and tone that they want out of and adventure and it is perfectly paced for a single 4-hour session. If you need a drop-in, drop-out game, or you want a game where you can rotate GMs, this is it.