5. 'Hitman: Blood Money'
The fourth Hitman game, Blood Money was the first to commit to nailing its central fantasy – that of being the ultimate assassin – with no distractions. Every level was simply an interesting space in which to kill. You were free to explore significant chunks of the level without drawing attention, and every target interacted with that space in some way. They might put on a pyrotechnics display or rehearse an opera, but they were never just sitting in a room waiting to die, making deaths that seemed accidental as feasible as silent gunshots or brute force. Blood Money set a standard every subsequent game about being an assassin would be held to.