Taking its inspiration from the gameplay of Serious Sam (rooms overcrowded by monsters), which concept is as old as Doom for the First Personn Shooter, Painkiller does not have the pretention to renew the genre. But its good level design, served by incredible graphics, made it a very fun action game.
Using all the Hell clichés, Painkiller offers to travel from medieval to modern times, and from lots of different places, like an asylum, a military base, a prison, etc... Such various situations allows us to discover a refreshing experience at every new level. But the inconvenience is that the game doesn't actually has a story. Painkiller is one of the first FPS which uses "achievements" to give us in game bonuses (slow motion, etc...). Another interesting plot is the fight against bosses, who are truly huge. Each of them proposes a different challenge, and simply fighting with them is so enjoyable that it could be considered as a reward.
Painkiller is the type of game very amusing to play, with a high level of realisation, but forget about the background.