A few levels have secondary objectives, which are not required to complete unless on the normal or hard difficulty setting.

Campaign seems too short at 15 hours, 20+ on hardest difficulty.

On harder difficulties, there are more objectives that must be completed before the player can progress.

After the credits roll, the player is free to continue playing on harder difficulties.

The game is known for its various bugs and hard difficulty.

The player travels through eight levels, each one increasing in difficulty, with the last three only being available on the harder difficulties.

On hard difficulty, however, he can die, which results in a game over.

The style now corresponds to easy, medium, and hard difficulty respectively.

Players can choose between easy, normal, and hard difficulties.

On hard difficulty, the game continues beyond that, with the true final stage.