Fridge Logic: In Returns. Considering that you got all of the game's animal abilities when you kill the man, why doesn't the Visitor just get inside the resulting Slashed Throat, absorb the man's genes and mutate into a humanoid form there and then instead of having to kill the woman to obtain them? Possibly because the man had been drinking copious amounts of alcohol which could have potentially weakened or killed the Visitor, or taking a large humanoid form would have made it a big target for the woman to shoot. Or maybe it just wanted to be a pretty lady. Or maybe to get female organs for it to reproduce.
Funny Moments: In the first game, you assimilate a cat. When the Visitor bursts out of it, the thing meows.
Narm: The monster at the end of the original The Visitor is pretty cheesy in appearance.
Squick: There's copious amounts of blood and gore in the games. And in the first game, there's one where you kill a cat... by entering from its anus.
YMMV tropes for the film:
Awesome Music: Franco Micalizzi's jazzy score is admirably restrained given the film's batshit insane subject matter, and often quite beautiful. The standouts have to be the killer main theme and "Sadness Theme". In fact, said score was awesome enough that parts of it were later re-used in Kill Bill.