Gun down the attackers as you grab keys to open the portal. Upgrade weapons, and get new ones.
Controls:
W,A,S,D / Arrow keys - To move.
Mouse key - To aim and shoot.
Space bar - To reload. Numbers 1-8 - To select weapon.
Q/E - To toggle weapon.
M - To use medical kit.
C - To show upgrades page.
P - To pause.