An amiable, affectionate homage to the sci-fi/horror B-movies of the 1950s—with a little Troma, "Killer Klowns from Outer Space," and the "Invaders from Mars" remake thrown in—"Slither" may be too tongue-in-cheek to break bank at the box-office, but it does its job well. Will mainstream genre fans recognize writer-director James Gunn's (scripter of 2004's "Dawn of the Dead") inspirations and be in on the joke? It's hard to say. Nonetheless, the film takes a stylish, back-to-basics approach to the material (with more effective practical effects than fake CGI, for example) and doesn't hesitate to throw everything in but the kitchen sink.

In the homely small town of Wheelsy—the kind of middle-America burg where nothing much happens and the police radar the birds for speed rather than the cars—what looks to be an alien meteorite crash lands to Earth. Out of it shoots a parasite that burrows into the stomach of sexually frustrated married man Grant (Michael Rooker) and works its way up to his brain. As physical changes begin to take over Grant's body and lovely schoolteacher wife Starla (Elizabeth Banks) starts to take notice, the alien's plot for takeover kicks into high gear. Infecting single mother Brenda (Brenda James) with his new DNA, Grant uses her as an incubator to create thousands of slimy alien slugs out to zombify the population. With no outside help to turn to, it is up to Starla, nice-guy police officer Bill Pardy (Nathan Fillion), foul-mouthed town mayor Jack MacReady (Gregg Henry), and teenager Kylie (Tania Saulnier) to survive long enough to save the day.

One of the last horror-comedies of this sort, 2002's "Eight Legged Freaks," had its moments of winking cleverness, but "Slither" is the stronger effort. Putting to use its R rating with some equal parts gruesome, gory and gooey moments, the film purees together the dramatic with the comedic with refreshing ease. Writer-director James Gunn, who not surprisingly cut his teeth working for Troma, treats the story with a seriousness that drives its lighter, more sarcastic side. Gunn rarely goes for cheap laughs, but finds humor all the same in his realistic view of how these characters—and ourselves—might react if we were ever faced in reality with aliens, parasites and zombies. One of the funniest scenes comes on the heels of the heroes seeing Grant's newly deformed, drippy, tentacled body. "He looks like something that fell off my dick during the war," one of the police officers candidly lets slip.

The cast excels because they all know what kind of movie they're in, and act accordingly. Elizabeth Banks (2005's "The 40-Year-Old Virgin") has the small-town look and sound down to a science as Starla, but adds further layers by expressing the confusion of being torn between the sanctity of her marriage and knowing that Grant is no longer the man she married. As Starla's old school chum and best hope Bill Pardy, Nathan Fillion (1999's "Blast from the Past") plays the straight man with mischievous hints of self-effacing humor. Best of all is Gregg Henry (2002's "Ballistic: Ecks vs. Sever"), an absolute hoot as the profane, tell-it-like-it-is mayor of the town Jack MacReady. He joyfully steals all of his scenes and gets some of the quirkiest lines of dialogue to run with.

Save for an extended sequence where Kylie must escape the parasites as well as the rest of her now-zombie family members, "Slither" isn't particularly scary. The movie also takes a little too long to get moving in the first act, causing the action-packed third act to feel abrupt and kind of anticlimactic. That the picture comes off seeming overly short is perhaps a good thing; at a reasonable 94 minutes, it might be that this potential cult item is so much fun that time just flies by. Whatever the case, "Slither" is a wickedly entertaining (if not groundbreaking) romp through conventions inherent from a more innocent time for the genre—rampant slaughtering of dogs, cats and farm animals not included—that all the while cooks up some imaginative, unpredictable beats of its own. Will "Slither" cause nightmares in the viewer? Probably not, but it will make a heck of a great drinking movie with friends.