Demonic Spiders: Literally! Giant spiders can leap through the air like grasshoppers and fire life-sapping strands of silk that pulls you towards them, in addition to leaving webs around that can also drain your health if you get caught in them, thus hampering your movement.
Most Wonderful Sound: The six "EDF" chants in the voice command list. If you're leading an AI squad, using it causes all of them to instantly chant "EDF" with you, as if on their own accord. Chants of EDF! EDF! will override all other voice lines and drown out all other sound.
To a lesser extent, if you have a squad, you can issue commands to them with the multiplayer voice commands. Granted, they won't actually obey them, but hearing them respond "Yes sir!" in unison to you at least makes you feel in command.
Narm Charm: Earth Defense Force 2025 is a giant love letter to the science fiction B-movies of the past. Naturally this extends to the dialogue; every line of dialogue is either purposefully overdramatic or completely failing to be dramatic. Most of this is due to EDF troops making macho boasts without the macho voice to match, making them come off like complete dorks.
Nightmare Fuel: The third trailer of the game introduces an enemy type that resembles the Asian giant hornet, the world's largest and dangerous hornets known to man.