Ever played that game? It's free, ya know. Google it.
In One Epic Knight, the player runs through a dungeon until they die. They collect money, weapons, shields, and other items. They dodge obstacles, bust into locked and blocked-off rooms, find secret passages, and fight monsters. Rewards are better the deeper into the dungeon players get, though the danger increases as well.
In Pixel Dungeon, the player runs through a dungeon until they die. They collect money, weapons, armor, and other items. They dodge Giant Piranhas, bust into locked and blocked-off rooms, find secret passages, and fight monsters. Rewards are better the deeper into the dungeon players get, though the danger increases as well.
Am I oversimplifying? Definitely. But the actual theme between the two is very similar.
Disagree? Certainly the gameplay is very different, but can you convince me that the THEME itself is different? Go ahead, give it a shot in the comments.