Arkham City, like its predecessor Arkham Asylum, is an open world action video game that incorporates elements of stealth and predator tactics. All of the gadgets previously obtained in the first game are present at the start of Arkham City (with the exception of the Ultra Batclaw, which is replaced with the regular Batclaw and Sonic Batarangs.) Most of them have improved or new capabilities; for example, the Cryptographic Sequencer can also track signals, the line launcher now has a feature that allows Batman to flip over and launch another zipline perpendicularly across, switching directions, the remote control Batarang now has a built in brake and boost, and the grappling gun can now be used while gliding to boost Batman further up into the air. Three additional gadgets have been revealed: smoke pellets to confuse armed enemies when spotted by them, the Remote Electrical Charge which is a sniper-like taser gun used to power generators and shock enemies, and ice grenades used to freeze enemies and make pathways through water. The game incorporates more puzzle elements; the use of Batman's "Detective Mode", which highlights elements such as enemy skeletons and clues on-screen, is used to perform forensic activities such as tracing the origin of a sniper round.
The player also has access to a criminal database that tracks the major villains across the city and the forensic puzzles much like the first game. However, Rocksteady's art director David Hego described the new detective mode as an "augmented reality mode", and game director Sefton Hill has also stated that although enemies and evidence can be seen more clearly, the navigational part is toned down as they found that some players completed Arkham Asylum using detective mode almost throughout the entire game. Optional challenges from the Riddler to collect hidden trophies placed around the city are also present, but require additional effort to locate, such as interrogation of men loyal to the Riddler, and the use of nearly all of Batman's gadgets to disable "traps" and barriers placed around them. After a certain number of trophies are found, Batman must go rescue a hostage that the Riddler has captured, which requires him to disable death traps set by the Riddler.
The player controls Batman, making their way around Arkham City to complete mission objectives. In addition to the primary mission, the game introduces secondary missions featuring a number of key characters and their stories. The player can opt to move silently, avoiding inmates and other enemies using a combination of gadgets to sneak up on enemies to incapacitate them. Batman's gliding ability has also been upgraded, allowing players to dive downward and pull themselves back up, making it much faster to move through the air. The grappling gun may also be used while gliding. At other times, the player may be forced to fight inmates using an improved version of the Freeflow combat system from Arkham Asylum, allowing for multiple simultaneous counters, the ability to counter thrown objects, jump attacks, powerful multi-strike beat-downs, upgraded Batarang and Batclaw attacks, and the ability to use gadgets such as the Explosive Gel and line launcher in Freeflow. Movement about the city is made difficult due to the formation of gangs and territory between rival villains, such as Two-Face and the Joker, that causes in-fighting that Batman must avoid.