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: Besides the Metal Spiders (which fit this trope nicely), Wasps (both normal and Metal variants) are also a source of annoyance to player. They are much smaller and faster than other mini-bosses, making it a pain to try to target them with a non-guided weapon. They have an attack that holds the player in one place until another soldier hits them. Finally, the metal variant possesses a powerful beam weapon that can do in excess of 200 damage with a full hit.
Game Breaker: The Battle armor's shield can withstand hits from anything that does damage. This includes the Pesticide weapons, which just zero out the energy meter and leave you without a scratch. Inferno mode just got a lot easier.
God Damn Bats: The gunships are incredibly annoying. They have little health, but are quit small and fast, making them hard to shoot down without lock capable weapons. To top it off they have two different attack modes. Their laser pulses during which they will strafe you on the ground in a attack run, usually while you're busy dealing with other problems, and a high powered laser they fire after they stop for a short bit before going back to zooming around. Now throw in multiple gunships doing that and it gets really annoying.
Ant hills. Without a decent weapon with large blast radius, it's very hard to shut it down. In fights with larger enemies, they tend to be an annoying distraction when you're trying to focus on the tougher enemy.
Which is why you suppress the Nest with heavy weaponry, as instructed by Intel and Ops. This forces the Nest into a sort of dormant, damaged state where it cannot spawn any bugs for a minute or two. Easiest with very heavy AOE weapons, like the Rav-Tech weapons from the Aerialist Munitions Package or the Tank's main gun. Usually keeps it shut long enough for you to clear out the nearby bugs and plant the charge.
Any enemy that can attack you while you're trying to plant a demolition charge on an ant hole as a an attack resets the progress bar.
Robotic Spiders. Their attacks hurt more and on higher difficulties can damn near kill you with a jump attack. They also spam their web attacks like the old spiders.
Hell Is That Noise: The buzzing of wasps and cyborg wasps. It's pretty hard to hear unless you turn the music off though.
Most Annoying Sound: The NPC atmospheric dialogue. There are not a lot of recorded lines and they get repeated constantly.
Most Wonderful Sound: The death sounds made by the spiders and cyborg spiders. It makes them so satisfying to kill, given how annoying they are.
They Changed It, Now It Sucks: A reaction from a subset of fans of Earth Defense Force 2017. Most of reactions are due to changes neccessarily made to the game to make it viable online. Features like the "ping pong" type physics of the bugs, the style of the explosions, and the way enemies hordes are handled.
Also, the shift in tone from a cheesy Japanese style to a cheesy American B-Movie style brought some complaints, too.