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: Insectia Scene 3 has the praying mantises. As soon as they see Bug gets near, they start clawing about in a frenzy, making it near-impossible for Bug to jump on them without taking damage. If you try to approach them from the back, they turn around. And they can last five hits before going down. Thankfully, that's the first and last time you'll be seeing them.
Splot has the snails from Insectia... except that they're now Made of Iron (they take the most hits of any normal Mook), and come equipped with a machine gun!
Insectia had bees. Aaaargh, Not The Bees! They tend to come in swarms and you have to time your jump exactly when they tried to rush into Bug. Some of them even appear out of nowhere on an otherwise deserted platform! Hope you had the Zap Cap equipped if you took the wrong route in Act 2...
Reptilia had Army Ants that fired out bouncy grenades from their tails. Plain annoying when placed at the top of an incline, as Bug would have to avoid the grenades while moving up.
Splot had mosquitoes and frogs. Mosquitoes could take quite a bit of damage, and came in even larger swarms than the bees in Insectia. Frogs would jump around randomly then try to swat bug with their tongue.
Quaria had starfish. Especially those that came in a neverending stream, bouncing down the inclines.
The Burr-ubs had snow fleas. These ANNOYING little buggers would 1. jump out of the snow and throw some ice at Bug before going back in 2. throw aimed snowballs from a distance 3. roll snowballs continuously until Bug got near, in which case they ran away.
Arachnia had spider enemies, the most irritating of which shot bowling balls at Bug. Also, the Mook that kept splitting into two smaller copies each time it was hit could be considered one.
It's Hard, so It Sucks: One of the reasons why those on the "hate it" side give as their reason for not liking the game.
Most Annoying Sound: EVERY. SINGLE. FREAKING. THING. that Bug says, really. Not helped by the fact that he's supposed to be a Mascot with Attitude. If there's a good reason why quite a few people hate the game, it's this one.
The good news is that you can turn off the voice acting. Phew.
That One Level: Again, Splot. There's a section where Bug has to jump from bubbles moving up and down over a Bottomless Pit. You have to time your jump exactly, otherwise you will fall to your death. There are eight jumps in all, and good luck making that last one.
Tropes for the film:
Critical Dissonance: While critics gave it good to average reviews (61% on Rotten Tomatoes), audiences almost collectively hated the film (being one of the few films to get an F rating on Cinemascore). But then again, the film was mismarketed as a horror film (it's really a psychological drama/thriller).