The answer to what makes for a great introductory RPG depends on what your goals are. Are you looking to get people hooked based on a well-known brand? Are you looking for exciting game mechanics to draw them back to the table? Are you looking for a straight forward game mechanic that’s easy for non-gamers to pick up?
The answer informs to game.
For me, the answer to several of these is Dungeons & Dragons 5th Edition, especially if you’re running pre-generated characters. Dungeons & Dragons dominates the role-playing landscape because most people – gamers or non-gamers – know about it. Depending on their age, what they know may be informed by misinformation (“isn’t that the devil worshipping game?”) or something their friend’s parents played back in the day. It may also be this cool thing that everyone’s been talking about, and hey, wasn’t there just an animated series inspired by D&D on Amazon?
Compared to previous editions of the game, it’s core mechanic is straightforward. Roll a twenty sided die, add or subtract a modifier, compare it to a target number. If you’ve got a pre-generated character in front of you, you can be playing in minutes. I’ve run multiple introductory 5e adventures over the years – for kids, for co-workers, at conventions, etc. Everyone’s easily picked up the game, and in some cases, continued running the pre-gen character for years! D&D also benefits from decades of fantasy tropes from novels, movies, video games, and well, pretty much every media in existence. That creates a referential shorthand that makes running the game (and describing scenes) a lot easier.
If you’re looking to hook players with a shot of adrenaline and excitement, while simultaneously exploring non-fantasy genres, Savage Worlds is a great intro game. While it has a bit more math than D&D, it has none of the tedious hit point tracking. It also has exploding dice, which means any die role can turn into an exceptional on (or legendary). An exploding die mechanic is one in which you re-roll a die when it comes up with its maximum value. That value gets added to your total, and you roll. If that die comes up with its max value again, that gets added, and you keep rolling. It enables spectacular stunts – I once say a player jump off a crumbling cliff to save another character, with nothing but hope and a few banked bennies (a game currency you can use to re-roll dice). And they did it!
Savage Worlds is the kind of game that hooks people the first time they play it, and while not everyone loves it as much as I do, it’s an excellent alternative to D&D. Plus, it has rules to run just about any genre. Granted, some genres work better than others (e.g. action/adventure works better than straight up horror) but the diversity of what it can support is impressive. All also add that Savage Worlds is a fantastic introductory game at conventions, particularly larger ones. There’s a robust fan community for the game, and they go all-out at conventions with detailed, 3D environments for their games. I’ve seen 3D tropical islands and pirate ships, complete with gummy tentacles to represent the sea monsters. They’re an impressive site that can’t help but pull in new players.
And finally, there’s Call of Cthulhu. Granted, my experience with introducing people to CoC is limited to a single game in college, but I think the principles still hold. Call of Cthulhu core mechanic is easy to learn (roll percentile dice; if you get under a target number, you succeed) and most of its character sheets are straight forward. While horror is at its core, the characters themselves are every day Joes and Janes. They’ve got day jobs and hobbies that people can relate to, and most people are familiar with the 1920s (when the game is typically run). It’s easy to turn a CoC game into a sort of murder mystery event, which people are already familiar with playing, and to augment it with a nice dinner (“You may wonder why I’ve gathered you all here together, on All Hallow’s Eve…”).