And last but so very, very far from least, we have the literal game-changer, Arkham Asylum. This was Batman's triumphant return to video games, and his best ever fair in the medium.
Before Asylum, we had gotten LEGO Batman and Batman Begins, two really good games. But neither was the huge, standalone Batman title that the character deserved. In stepped Rocksteady.
Due to the lukewarm reception of many previous Batman games, few were excited about Asylum. Most of us were at least keeping expectations in check. So when the game released in 2009, it blew everyone away. It's easy to forget how monumental this game was, because every Batman game before it had been good at best, and awful at worst. But this wasn't just an exceptional Batman game, it was just a brilliant game full stop.
So while Arkham City, and presumably Arkham Knight, improved upon the formula and rank higher in some lists, Arkham Asylum was the one that changed everything, gave Batman the game he had always deserved, and started something pretty special.