Species/YMMV

Evil Is Sexy
Fridge Brilliance: In the first movie there's a closeup of Sil in John Carey's garden where she blinks and we see that she has nictitating membranes in addition to "normal" eyelids. You thought that was just there because it looks cool and alien. Nictitating membranes are a feature possessed only by semi-aquatic tetrapods, so her having them is a subtle indication that she can function underwater for prolonged periods, foreshadowing the scene at the film's climax where she hides underwater to elude the heroes.
Hilarious in Hindsight: One of Sil's victims in the first was named John F. Carey. The 2004 Presidential candidate was John F. Kerry, who was a well-known senator at the time of the movie.
Karmic Death: Fitch in the first film, given how he had instigated the events to start with.
Sequelitis: First film is considered either OK or So Bad It's Good. The following ones aren't so lucky.
Special Effect Failure: The aliens prosthetics in Species III are vastly inferior to what was seen in the two previous films. The Awakening has similarly bad effects, but for the most part it does a better job of working around them.
- In the first film, the "mist" in the woods outside the hot tub guy's house is patchy, obviously from a smoke machine. Also the Conspicuous CGI when she is shot at the end.
Straw Man Has a Point: In the first film, Xavier says they made her female assuming she'd be more docile - but they actually may have bought themselves more time, considering they may have had a serial rapist on their hands if it were male.
Unfortunate Implications: in Species II when Marg Helgenberger's character says that Eve shouldn't be held responsible for her actions and is human too, one of the other characters rebuts her by pointing to the cocoons of the infected astronaut's metamorphosizing offspring and saying "like them". Keep in mind, as far as we know the infected astronaut's children haven't actually done anything bad yet (well, aside from killing their mothers, but that's like holding a human responsible if his mother died in childbirth). Our heroes are about to slaughter them in their sleep purely because of what species they belong to. I'm not saying this isn't justifiable under the circumstances, but if you can have sympathy for Eve you can have sympathy for them. But when they're up there in those cocoons they look obviously inhuman, and that means it's obviously OK to kill them. In the movie they all seem to be portrayed as male, so one suspects a degree of The Unfair Sex is involved as well.
Visual Effects of Awesome: There's no denying Species II had some pretty awesome scenes.