If your cheater's heart wants you to use cheat codes, create a shortcut of the game (to *.exe file) and edit its command line with the expression +set com_allowConsole 1. Now you can use the console to enter cheat codes, which will help you to make the process of the game more exciting! To call the console window press Alt+Tab+~ or ~. Since you've done this, you can enter any cheat code you like while playing the game.
god: god mode
noclip: toggles clipping mode
undying: you become undying!
listcmd: gives you a list of all commands
listcvar: shows you all cvars
listentities: shows you all entities
listmonsters: shows you all your enemies
Use the command give <option> to get more abilities!
all: get all items and weapon
armor: get all armor
health: refill you health points
ammo: refill your ammunition
Use the command spawn <option> to get any weapon you like from the list below!
weaponmod_hyperblaster_bounce
weaponmod_lightinggun_chain
weaponmod_machinegun_ammo
weaponmod_nailgun_power
weaponmod_nailgun_seek
weaponmod_nailgun_rof
weaponmod_nailgun_ammo
weaponmod_railgun_penetrate
weaponmod_rocketlauncher_burst
weaponmod_rocketlauncher_homing
weaponmod_shotgun_ammo
If you want to save your time or you are too bored with a particular level, you can easily skip it! Just enter any cheat code from the list below in the console window.
airdefense1: Air Defense Base (beginning of game)
airdefense2: Air Defense Trenches
convoy2: Aqueducts
convoy2b: Aqueducts Annex
convoy1: Canyon
walker: Construction Zone
network2: Data Networking Security
network1: Data Networking Terminal
process2: Data Processing Security
storage2: Data Storage Security
dispersal: Dispersal Facility
process1: game/process1
storage1: game/storage1
hangar1: Hangar Perimeter
hangar2: Interior Hangar
mcc_landing: MCC Landing Site
core1: Nexus Core
hub2: Nexus Hub
hub1: Nexus Hub Tunnels
mcc_1 Operation: Advantage
mcc_2 Operation: Last Hope
building_b: Perimeter Defense Station
putra: Putrification Center
recomp: Recomposition Center
medlabs: Strogg Medical Facilities
core2: The Nexus
tram1: Tram Hub Station
tram1b: Tram Rail
waste Waste: Processing Facility
Note that you can not only skip levels but also you can skip those annoying movies! To do this you need to edit the command line of a shortcut again (the information about the shortcut has been mentionned above). Add +disconnect to the command line and enjoy the process!