This also includes story-related activities. The story walkthrough will tell you the basics to each mission. On harder difficulties, you are generally faced with more enemies with better accuracy and more health, whilst you are more susceptible to damage. This walkthrough will guide you through the game as if you are playing on Casual difficulty. The difficulty can be changed at any time by pressing Start and selecting 'Difficulty' from the pause menu. If you want to complete the game as quickly as possible, select 'Casual'.
The game is not that difficult, especially when you begin earning money to purchase many of the upgrades, so choose whichever difficulty you think will be most enjoyable. To begin the game, select 'Campaign' from the title screen and choose 'New Game'.
