Caan plays veteran detective Matt Sykes, determined to catch the bad guy who killed his black partner. What makes this different from the usual buddy movie is that Caan's enemies are aliens, and so he needs a new alien partner to help catch the villains. Matt's new sidekick is named 'Samuel Francisco' (Patinkin), one of an alien race being integrated into regular society after their slave ship arrives on Earth. These aliens struggle to fit into human civilisation, facing greater prejudice than foreign refugees because many of them act too eager to please - having previously lived a hard life as slave labourers. This, coupled with important fact that the 'newcomers' (also dubbed 'slags', without explanation) have no sense of humour, means they annoy a lot of people - including Matt.
Going into the ghetto community of Slagtown to track down a cop-killer alien, Sam (hastily renamed George!) helps Matt understand the newcomer culture but keeps some discoveries that are relevant to the case secret from the human cops. Harcourt (Terence Stamp) is a wealthy and highly respected alien among men, running a chemical lab to make powerful and addictive drugs for illicit sale to other aliens. We can guess that he's behind the film's central plot because he's so smarmy you instantly want him shot dead (preferably in a violent battle with human cops). The stereotyping of alien characters with wholly human traits is one aspect of Alien Nation that dates this movie. Nowadays, a creative effort (at the script stage) would try to identify something entirely non-human about the newcomers, as a race, which makes them unique - instead of just having them adopt all mankind's flaws.
There are jokes at the expense of both humans and aliens. The newcomers get drunk on sour milk, and seawater burns their flesh like acid, but in one amusingly played scene between Matt and George (alias, Sam, remember?) we learn that the aliens may have substantially bigger dicks than men and, despite their difficulties understanding comedy, the slags prove to be physically much stronger - due to genetic origins in slavery. When Matt questions an alien female at a strip club, there's a question of whether he can get away from her without being raped.
However, nothing much is made of the potential for drama, horror or slapstick these ideas offer. Caan and Patinkin work hard to make their characters likeable, and Stamp does a decent job as their ambitiously menacing antagonist, but even actors of their calibre fail to save this film from succumbing to mediocrity at times. The director Graham Baker made The Final Conflict (the third Omen film), underrated thriller Impulse (1984) and, more recently, Beowulf (1999). Clearly, then, he's not top of the class as a genre filmmaker. What's interesting about Alien Nation is that it was successful enough a get a spin-off TV series, and the TV movies (directed by Kenneth Johnson) following it were able to explore some of the SF ideas Baker's so-so effort ignored. Ultimately, this is a B-movie with an A-list cast. For superior aliens-in-our-midst comedy thrills, see Carpenter's They Live, made the same year.
DVD extras: featurette (seven minutes), behind-the-scenes footage (four minutes), a trailer, TV spots, scene finder (16 chapters), 13-language subtitles.