One of the highlighting points of the game will always be the amount of time taken by a player to finish the game. It encourages the competitive spirit in players. The timer starts off at the first level and keeps counting until the player defeats the boss enemy.
As the player progresses onto the next level, the enemies become stronger and harder to defeat. So, the player has to adapt to those changes and play accordingly. It just allows the game to be more realistic.
When Romero was injured, he was fit with a television on his head to stay alive, during that process he also got the powers of shooting digital signals. These digital signals help Romero to defeat the enemies which are static signals approaching his way.
These are the enemies that prevent Romero from reaching the goal (i.e his girlfriend). They shoot him with static signals which can damage his brain and kill him.