Movies based on video games tend to be monstrous globs of disparate parts, all stitched together into awful, lurching melanges. They draw elements from their source material in order to please the game?s fans, but must force these elements into traditional film formulae so as not to alienate the casual viewer. But “Resident Evil,” based on the series of zombie-blasting survival-horror games, which were in turn based on classic zombie films such as George Romero?s “Dawn of the Dead,” fits the film medium better than most other attempts.

The games and movie both follow the sordid exploits of the sinister Umbrella Corp., a massive corporation which, aside from more traditional commercial aspects, invests itself heavily in genetic engineering and biological weapons development, which pursuits form the fulcrum of the story.

The film opens with a hazard-suited figure in some kind of lab carefully loading several small vials of blue and green liquids into a shielded case. On the way out the door, whoever-it-is tosses an extra vial onto the ground, sending vapors wafting through the lab?s air-conditioning system. This doesn?t sit well with the facility?s internal security system, which efficiently kills the building?s entire population of workers, gassing some, drowning others and dropping a few elevator cars full of passengers down their shafts for good measure.

Cut abruptly to a naked woman just waking up from a nap in her running shower. Here?s our heroine, Alice, played by Milla Jovovich of “The Fifth Element,” who can?t remember who she is just now. Wandering around the house a bit, ? a reference to the mansion setting of the first game ? she finds suspicious things such as a cache of locked-up weapons and a man in civilian clothes named Matt (Eric Mabius) who says he?s a cop, followed by a troop of black-clad paramilitary types crashing through the windows in a scene whose only real purpose seems to be to break a lot of glass.

These commandos, of course, work for Umbrella, and they seem to know who the girl is. They drag her and the “cop,” along with them to an underground railroad, where they find another memory-lapsed man, Spencer, (James Purefoy) unconscious in a locker, and explain that our amnesiacs have been hit by a spray of nerve toxin, which was why they passed out and can?t remember anything now. The railroad leads deep under neighboring Raccoon City to “The Hive,” the facility from the film?s opening. The Hive?s governing artificial intelligence,”Red Queen,” has gone berserk and the troops want to find out why.

And so they do. Trekking to the bottom of the facility, the group finds an ominous room full of refrigerated chambers and piping where a dining hall should be ? there?s something going on here that these intrepid few weren?t briefed on. Reaching the corridor leading the Red Queen?s core, about half the group is literally taken apart by the computer?s booby-trap defenses, leaving our three main characters and a handful of the commandos to take care of business.

Ignoring threats of imminent death by the childish holographic Queen, the group?s tech shuts the A.I. down, which is a mistake, naturally. Resetting the facility?s computer unlocks all the doors, letting forth the hordes of undead workers trapped within the building?s rooms. Seems that vial of liquid is the cause of all this trouble. It?s called the “T-Virus,” and it reanimates its victims, instilling in them basic motor control, a ravenous hunger and a weakness for head trauma ? a weapon of questionable effectiveness, to be sure, but highly infectious ? the Queen killed the lab workers to prevent spreading the virus to the upper world.

The rest of the movie is filled with escape attempts and grisly deaths of the surviving humans, with backstory filled in by convenient flashbacks on the parts of Alice and Spencer and by Matt, who is not at all a cop. The cast is whittled down to the horror-movie requisite of two survivors, but there?s no real mystery as to who lives through the ordeal and no reason to really care much about the characters; they?re just sheep, really, and the only question at hand is which bleating hunk of meat the shambling, moaning wolves drag down next.

The apathy isn?t because the acting is bad, though it isn?t particularly good, either. There are fairly good turns by Jovovich and Mabius and by Michelle Rodriquez, who plays the hyper-macho, tough-as-nails and profane female soldier who has turned up in every desperate action-horror movie since “Aliens.” The problem is that there?s no depth to the characters. This can be excused to a point in the case of Alice and Spencer; they have no memories for most of the movie, save Alice?s dormant fighting skills, but the rest of the characters are awfully thin. It?s hard to care for the fates of paper dolls.

There are some excellent scenes, though, both in the realm of suspense sequences and the big-money creature scenes, though the zombie hordes are a bit dull. A pack of mutated guard dogs with shredded, oozing coats makes for a tense encounter, as does the movie?s set-piece, a monstrous take on the game series? “Licker” creature, a skinless, whip-tongued abomination that serves as the final “boss” of the film. Also good is a false ending that leads into a cheerfully blatant set-up for the planned sequels.

As a movie, “Resident Evil” is entertaining, but nothing special. As a game-to-movie conversion, it succeeds because its source story is just the right fit for an action movie, unlike last summer?s “Tomb Raider” or the 1990s takes on “Street Fighter,” “Mortal Kombat” and “Super Mario Bros.” All these tried to stretch extremely thin and sketchy plots to fit a feature film, and failed. “Resident Evil” succeeds because the games have enough of a story to shoehorn into a film, without having to stretch to fit. If the characters had broken the horror-action mold a bit, and some depth added to them, it could have been a horror classic.