Batman: Arkham Origins is an interesting prequel to the rest of the series, but its original pitch was more ambitious, involving playable villains.
WB Games Montréal's prequel already stands out from the rest of Rocksteady's Batman: Arkham games, but it almost gave the player control of its many villains. For the most part, Arkham Origins plays just like the other games in the series, and even has better boss fights than Arkham Knight. The original pitch for the game apparently included playable villains, where players could explore the open world of Gotham with different abilities and traversal mechanics.
When it released in 2013, Arkham Origins had a daunting task of living up to the two predecessors that were already out at the time - Asylum and City. Arkham Asylum had set a new bar for superhero video games, and City expanded on it in nearly every way. While players waited for a third Rocksteady game, WB Games Montréal delivered a prequel which saw the Caped Crusader still in his early days of vigilantism. A mass breakout from Blackgate Penitentiary leads to eight of the world's deadliest assassins seeking a bounty on Batman's head.
While many felt Arkham Origins didn't quite live up to Asylum and City, it is by no means a bad game, and isn't even the worst game in the Batman: Arkham series. It's plot is rather interesting, and excelled in making compelling boss fights. According to game direct Benoit Richer in a now-deleted Twitter exchange (preserved on Reddit by user MohamedZano), the original vision for Arkham Origins was much more ambitious than the final product.
Unfortunately, details on the original pitch for Arkham Origins are extremely light. Richer doesn't offer any more information beyond his "original pitch where big parts of the game was playable villains in the open world to contrast with other Arkham titles." This certainly would have been a departure from the rest of the series, where playable characters other than Bruce Wayne are few and far between, like in the very good opening sequence of Batman: Arkham City. Different playable characters are mostly reserved for the series' DLCs, and the larger idea for Origins clearly didn't make it very far past the pitch stage.
The idea is very interesting, though, and Origins definitely would have had some interesting villains to play as. Deathstroke, Cobberhead, Bane, Firely, and Deadshot all would have been a fun departure from the Bat. Firefly especially could have given players a chance to fly around Gotham in a manner other than Batman's grapnel and gliding technique. Some of the other assassins, like Deathstroke and Copperhead, could have offered a lot of variety in the series' signature Freeflow combat. Regardless, Origins turned out to be a worthy entry in the Batman: Arkham series, and now WB Games Montréal gets to flex its creativity in development of Gotham Knights.
Source: Reddit