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 takes sadistic pleasure in shooting up his small town. He offers some justification by speaking about overpopulation, and how we should kill people to help curb the consumption of resources, but his attitude toward his victims shows that this is merely a shallow pretext. He shows a lot of joy during his massacre, and mocks his victims as they beg him for their lives. After he is finished, he murders his supposed best friend and frames him for the rampage, while he takes the thousands of dollars he stole during his attack and skips town with the intention of funding more rampages.
Hey, It's That Guy!: Fans of Ginger Snaps, keep your eyes open for Katharine Isabelle in a brief appearance as a beauty salon employee. The guy that plays Bill was also in both the sequel and prequel of Ginger Snaps.
Special Effects Failure: Generally averted, but the guns Bill is carrying have a tendency to change between shots - a gun that's obviously a MAC-10 in one scene has magically morphed into a Micro-Uzi the next scene and so on.
Maybe he has multiple guns?
There actually are no gun-switching goofs. One of the weapons Bill wields, a Ruger MP9, looks like a hybrid between a MAC-10 and Micro-Uzi. See for yourself, here.
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...