These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Demonic Spiders: Every vehicular Mook that is not a cabbie and not in a passive state is this in any level (even in the first map), but particularly the hover-trucks with their rear turrets in the fourth and last maps as they can constantly peddle you with highly damaging bullets if you manage to come close to them.
Game Breaker: The shotgun starting with the second level and available from that point on is absurdly powerful and can destroy just about any enemy in the game. Even the bosses will go down after 3-6 shots from the weapon. And it's rather ammo-efficient and laughably dirt-cheap, despite carrying only a maximum of 35 shells.
Goddamned Bats: The Ax-Crazy pedestrians and trap-door goons out of nowhere who riddle you with machine gun fire to pester your life.
Older Than They Think: Quarantine introduced a few key features prevalent in the game that would later make the Grand Theft Auto and Saints Row series popular: non-linear missions, drive-by shootings, gaining fares, weapon upgrades, a repair system, etc. However, thanks to the controversy surrounding its content at the time and how painfully difficult it was, the game was largely ignored and reduced to cult status. The only you can't do is get out of your car, a feature that is sorely lacking when compared to the later more popular franchises that were influenced by this game. Justified in this case because setting foot in the streets of KEMO can get you killed extremely quickly, as judged by the instantaneous deaths of pedestrians who get hit by any weapon thrown at them or hover-vehicle coming through.
The two boss missions that involve a guy wearing a powered-suit in the form of a bloated housefly. He constantly flies around to make your aim miss and his bullets can tear through your armor quick even with the best armor upgrade bought for that particular level. You need a gatling gun to deal with him since he moves very quickly and the shotgun isn't effective in stopping him despite the firepower. Thankfully, the two boss missions that involve him occur in two different levels: the second and fourth.
The final mission in the final level. You must deliver a plutonium-laced bomb to the headquarters of Omni Corp so that it will blow up the building and be razed down. Problem is, the building is located in a section that has its roads shaped in a spiral pattern, and the Mooks and traps there can quickly blast your cabbie to shreds even with the best armor attached. And once the mission is completed, you'll have to find out how to get out of the spiral mazed section without dying, as likely your protection is gone thanks to those now Demonic Spiders of hover-cars. It is highly recommended that you must be completely kitted out with the best weaponry and armor before taking this mission and Save Scumming is required in order to not die.