Keen players often have the well-known games already, so it’s worth a word with whoever they play with first.
If they mostly play with one other person, start here. Each of these is best given by that person, along with the promise of a first game.
For people who’d rather win or lose as one. The short ones allow very little talking; the long one fills a whole evening, with an app telling the story.
Easy to teach and fine for mixed company, from a family evening to friends who don’t usually play.
For someone with a regular group who likes heavier games. Arnak is a gentle step up; Gloomhaven asks for a group that meets every week.