At the beginning of the game you have a poor-quality pistol, and you can't transport yourself to the upper or lower hallways, you're trapped in the central one. However, as you play the game you will be able to earn money to buy all sorts of improvements.
The most important upgrades are those that allow you to move between hallways, which is vital to doing anything worthwhile. However, it's also a good idea to buy upgrades for your pistol, or even new weapons like a shotgun, which make things a lot easier.
You will also find different scenes and characters in Hold Fire. In the first level you play an average guy in an office building, but in the second level you're a knight in a castle.
Hold Fire is a fast-paced, very fun game where players rely on their reflexes to progress through the game.