Only 3 campaigns, with somewhat varied gameplay. The enemy density is rather high so they endlessly respawn, making most weapons a slog. Fortunately there are plenty of explosives to choose from, and they're the only realistic option for beating this campaign.
An alien race has come to take over Earth. They have suceeded to make humans their slaves. Only a few renegades, freedom fighters are left to destroy the aliens and bring peace back to the land.