It's a big complex tactical/strategic board game! It's only like a role-playing game in that you have persistent characters who have stats and level up. You don't really get to make decisions for a character like you would in an RPG (your character's actions outside of combat are often determined by random chance), and there's no freewheeling negotiated creativity; the choices are all mechanical in nature.

The game takes place over in-world "years" that take an hour or two apiece to play through. A winning campaign can last 20-30 in-game years; a losing one will tend to collapse well before that, but still might make it to the 10-year mark. So we're talking dozens or hundreds of hours depending on how dedicated you are!