Larian Studios might have blown everyone away with Baldur's Gate 3, but the colossal success of its fantasy RPG didn't come out of nowhere. BG3 was built on the shoulders of Larian's previous game, Divinity: Original Sin 2, a fantastic RPG in its own right, and one you can currently grab for a fraction of Baldur's Gate 3's price.
Set in Larian's homebrew fantasy universe of Rivellon, Original Sin 2 puts you in the role of a 'Sourceror'. You start the game captured by a Witchfinder-y faction called the Divine Order, who imprison you in a castle known as Fort Joy. Luckily, you can talk to God, as can all your mates. Things escalate in suitably fantastical fashion from there.
Much of what Baldur's Gate 3 became so celebrated for was first implemented here. For example, Original Sin 2 has origin characters, like Lohse, an enchantress with a demon stuck in her head, and Fane, an undead, skeletal Necromancer who has to disguise his identity to stop everyone he meets from freaking out. It also introduced the environmental combat system that lets you combine elemental effects with different surfaces, like chucking a fireball at a pool of oil. If anything, Larian toned this particular system down for BG3 to fit it into the D&D mould, so it's worth checking out Original Sin 2 to see what it looks like fully unleashed.
Original Sin 2 also shares BG3's drive to facilitate the player's role-playing whenever possible, giving you lots of different options to complete quests and solve problems, whether that's through extensive narrative choices, or futzing around with its flexible RPG systems. The main differences are that Original Sin 2 lacks BG3's flair for the cinematic, and the broader structure isn't quite as astonishingly reactive. It's also smaller, although you'd still be pushed to see all the interesting stuff in less than 100 hours.
In short, Divinity: Original Sin 2 was our 2017 Game of the Year for a reason. If you jumped straight into BG3 and are now hankering for something similar, this is the closest you'll get. And you'll pay a lot less for it at the moment too. GOG has it at a 70% discount, bringing it down from £30 to just £9. That's a fantastic price for an RPG this good. And don't be confused by the "Definitive Edition" subtitle – that just means it includes all the post-release updates Larian added to the game.
