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: Ignoring the actual spiders (though the Robot Spiders certainly fit this trope nicely), Wasps (namely Cyborg/Robot Wasps) border on this and Boss in Mook Clothing. They are much, much tougher than most mooks even on Normal, and whilst they hover in one place a lot they also move very rapidly when they aren't hovering. They also have an attack like the Hunter from Left 4 Dead, pinning you to the ground and making it so you can't fight back as they hit you repeatedly. Finally, the cyborg/robot variant possesses an extremely powerful beam weapon that can do in excess of 200 damage with a full hit despite looking more like the Gunship's altmode laser.
God Damn Bats: The new gunships are incredibly annoying. They fly faster and have smaller target profiles making them harder 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.
The Ants coming out of an anthole you're trying to destroy. They come out faster than you can kill them. They are also present for fights with larger enemies providing additional threats and are a nuisance 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 short time. Easiest with very heavy area 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.