Based on a manga that’s literally dozens of volumes long and still going strong, the Japanese action epic Gantz has a premise both unique and head-scratching as its title. Students Kei (Kazunari Ninomiya) and Kato (Kenichi Matsuyama) meet an untimely death via subway car, yet are transported at the point of impact to what seems to be an alternate dimension.

At any rate, it’s a sterile-looking, unfurnished apartment, barren but for the giant black ball in the room’s middle. The sphere is to this film what the monolith is to 2001: A Space Odyssey: one big mystery. Via textual cues, it informs Kei, Kato and the few other perplexed newly dead peeps with them — naked cutie (Natsuna Watanabe) included — that they are to suit up, grab a gun and play its game.

In basic terms, that’s ridding Japan of aliens, which take on wildly varying forms, from onion-headed mutants and a clockwork robot to statues that come to life, all of which the players shoot with powerful, energy-pulse weaponry that results in exaggerated explosions of gore and grue. Die in the timed game, and you die for good; survive, and you can return to your former life, but remain at the ball’s nightly beck and call.

Combining elements of horror and sci-fi — and initially reminiscent of the great Cube — Gantz is a high-velocity thrill ride with only slight lulls between rounds of go time. Like many effects-driven Asian films, it’s a little too long, but it certainly delivers bang for your buck, not to mention some sly laughs and more than a few WTF moments. The two-hour affair doesn’t offer closure so much as a breathing point before the forthcoming Gantz: Part II, and I’m perfectly primed for another leap into its imaginative world. In the meantime, I’m intrigued to the point of seeking out the comics. —Rod Lott