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.
Complete Monster: Bill Williamson is a sadistic domestic terrorist who takes great pleasure in committing large-scale acts of violence. He attempts to justify his actions by claiming to be a revolutionary who's just doing what he has to in order to fight overpopulation and government corruption. However, the way he acts towards his victims reveals this to be a shallow excuse. He shoots up his small town in the first movie, and wracks up a body count of over 100. He enjoys every minute of this massacre, and mocks the people he kills as they beg for their lives. Several of his victims die simply because they inconvenienced him in some way prior to his rampage. Afterward, he kills his supposed best friend and frames him for the act while he skips town with a bag of money he stole during the attack. In the sequel, he takes over a TV studio. He kills several of the hostages he takes based on assumptions he makes about their lives. When one tearfully tells him that he killed her sister in his previous rampage, he responds by mocking her crying and taunting her. He then forces a male hostage at gunpoint to beat her up. After his demands are met, he lets the hostages go, only to kill them and everyone else in the immediate area by blowing up the studio while he escapes. In the final scene, he gives a little girl a gun and encourages her to go home and kill her parents before committing suicide. Claiming to do what he does for the good of humanity, Bill's utter enjoyment of the violence he causes and completely unnecessary acts of sadism out him as nothing more than a mentally disturbed psychopath who kills purely for the fun of it.
Base Breaker: Rhett from Total Destruction. Some fans like him because he can jump high, is quite agile and speedy, and just looks pretty cool like several of the monsters. Others think he's a Replacement Scrappy for Curtis from Through Time and Universal Tour.
World Tour has the small robots called Fryborgs. They look like Goddamned Bats, but they take quite a few hits to destroy, and if you ignore them for too long, they'll easily chew through your health with their machine gun attack. It doesn't help that they launch their flamethrower attack at you the second after you hit them, which is very hard to dodge.
The same game also has Beetleborgs. They're gigantic walking robots that will slowly approach you and promptly bash you in the face. They're hard to kill, it's hard to dodge their attacks, and even if you do destroy one, they devolve into the regular sized robot mentioned above. It is however, possible to deal with them easily be using repeated jump kicks, and their slow speed means they're easy to avoid.
Flamer Dudes are much harder to hit than the helicopters, much more durable and do more damage, and they can knock you off of a building.
TANKS. They go down after three hits, but a single shot from a tank will knock you down or knock you off a building. And they rarely ever stop firing; chances are, the second you get up, you'll get knocked right back down...
Bombers are the flying version of tanks. They go down after one punch/kick, but they fly really fast and their bombs will instantly knock you off a building.
Flamer Dudes from World Tour. They're soldiers flying on jetpacks and carrying a huge flamethrower. They die after only three hits, but their attacks tend to set the monsters on fire, which leads to them falling off a building.
Super Flyers from World Tour are a cross between this and Demonic Spiders. They're weak, but their laser can drain your health if you ignore them for too long.
They Wasted a Perfectly Good Character: Total Destruction has thirty playable monsters, hell, forty on the Wii, including old favorites Vern, Ruby and Boris! It's a shame that there is close to no distinction between the different them outside of appearance and a few small attributes. A borderline example of why we have Quality over Quanity.
Viewer Gender Confusion: To this day there are still some fans who think Lizzie and Ruby are guys. Doesn't help that they sound gruff and were designed to look masculine...