Battle out of Hell, which requires the base game, takes place directly after the events of Painkiller. Daniel Garner has just defeated Lucifer and finds out that Alastor has taken over the armies of hell. In ten new singleplayer levels, with notable locations such as an orphanage, a ruined city, the zombie-infested Leningrad and an amusement park with a wild roller coaster ride, you have to prevent Alastor from attacking the gates of heaven.
For replay value, there are different goals while playing: finishing the level, meeting different challenges (kill a certain number of enemies, use only one weapon) and specific goals such as collecting all secret items or smashing every object. Meeting these challenges gives you black tarot cards with special abilities. Each level also has a batch of new enemies.
Two new weapons with dual firing modes have been added: the Boltgun/Heater and the SMG/Flamethrower. Additionally, the graphics engine has been updated for the expansion as well as the base game.
The awkward netcode from the original game, which has been rewritten for the Painkiller: Hell Wars Xbox version, has been implemented in this expansion pack. Two new multiplayer modes have been added as well: Capture the flag and Last man standing.
Painkiller's proprietary 3D engine is called PAIN. The base game uses version 1.0, the expansion has the improved 1.5 version. The physics are handled by the Havoc 2.0 engine, just like Half-Life 2
On April 30, 2005, both US and European English versions of Painkiller: Battle Out of Hell were put on the infamous German index by the BPjM. For more information about what this means and to see a list of games sharing the same fate, take a look here: BPjS/BPjM indexed games.
All blood and gore effects were removed or replaced with green blood. Also the first level (orphanage) was renamed to a "Herrenhaus" (manor) and the zombie children were replaced with regular demons.
The music heard during the level Leningrad is the national anthem of the USSR.
The first level, The Orphanage, is a big shout out to other horror-related games.
The 7th Guest and The 11th Hour: the first room has a layout just like Mr. Stauf's mansion. The stairwell is pretty much identical as well.
Grim Fandango: at the top of the stairwell, you'll see a message "In case of Zombies, Call Grim Fandango".