In Deadfall Adventures, the protagonist is an archaeologist adventurer who has a cheeky female sidekick, visits various places all over the world in search of the artifact Heart of Atlantis and fights evil Nazis/Russians in the process. So obviously the hero is... James Lee Quatermain, nephew of the novel figure Allan Quatermain. Similarities other action heroes aside, the story and dialogues are tongue-in-cheek and deliberately use the typical B-movie clicheès.
The game itself alternates between action and puzzle-solving sequences. The action part is a typical first-person shooter: James walks around and shoots everyone who moves before biting the dust himself. Besides the human enemies, there are also mummies which should be weakened by blinding them with the flashlight. Later in the game there are also traps in the environment which can be triggered to damage enemies.
The puzzles are mostly of the usual switch (using the interactive elements in the correct order) and trigger (finding the correct element to use/shoot) variety. Other examples are light beam puzzles or choosing the correct floor tiles to walk on. Allan's old notebook serves as in-game puzzle help; the separate puzzle difficulty setting controls how much it reveals. By finding hidden treasures in the linear levels, James unlocks the opportunity to buy upgrades like more health or faster reloads.
Multiplayer offers the usual competitive modes like deathmatch or capture-the-flag, including classes and level unlocks, and a co-op surviving mode in which players have to survive mummy assaults.