1. The movie storytelling formula is broken. Screenwriters are told to make audiences care about characters by jamming those characters full of bloated backstory and tedious monologues. In terms of garbage filmmaking—by which I mean in terms of Skyline—screenwriters need to realize that the modern audience doesn't need six overt reminders in the dialogue that a character is pregnant; we have spent our whole lives watching movies and we understand a young female character is pregnant when she vomits in the morning. We get it; move on. We have seen this kind of movie a thousand times before, and your job is not to linger over the same basic four pieces of information again and again. Your job is to drown us in information, give us way too much to understand.
2. A good science fiction movie (and here I also mean a good bad science fiction movie) cannot solely rest on one premise. A good science fiction movie has to hint at a world outside the edges of the screen. It needs to present a new good idea every ten minutes or so. I'm not talking about twists. I'm talking about exploration. Science fiction movies are about exploration. You can't linger over the same ten feet of fallow ground—aliens are attacking and they're very powerful!—for nearly two hours. Give us more.
3. Skyline is basically an episode of a sitcom—Seinfeld if we're feeling generous, Friends if we're not—with all the comedy stripped away. A bunch of douchebags are in an apartment and they argue about whether they should leave the apartment or not. Where a clever script would convince us that we should care about these douchebags, we are instead given a series of recursive arguments about leaving the apartment. In both the sitcom and Skyline, the actors stay in the apartment more often than not, usually because of budget constraints.
4. The special effects in Skyline are very good. This is because the directors are special effects wizards. (Curiously, some of the characters are special effects wizards, too, but the lame script never manages to make even one solid joke about this. That is practically a criminal violation of basic screenwriting rules.) Unfortunately, due to the problem presented in point 3—the inability of our characters to leave the apartment—the special effects are presented almost entirely as tableaus to watch. They're not interactive. The characters look through a telescope and then we witness forty-five seconds of what would be a phenomenal video game cut scene. And then we're back inside the damned apartment again.
5. The fucking movie ends exactly where the second act of a decent sci-fi thriller would have started. This is inexcusable, and it's the greatest of Skyline's many failures.