“The Matrix Reloaded,” the much salivated-over second chapter in the Wachowski brothers’ ambitious and technically envelope-pushing sci-fi trilogy, has great special effects–not to mention more suspense, sex, romance, heroism, villainy and drop-dead style than 10 movies of its kind. What it does not have is an ending.

Mind you, this is more a quibble than a complaint. As anyone who saw the first film 17 times (and probably everybody else) knows, writer-directors Andy and Larry Wachowski followed the success of “The Matrix” by embarking on back-to-back sequels. (Currently in post-production, “The Matrix Revolutions” is due out later this year.) The result is that “Reloaded” isn’t so much a movie, in the sense that there’s any real closure, as it is half a movie.

But, oh, what a satisfying half a movie it is, if for no other reason than the fact that the film’s two central action set pieces are brilliantly done.

First is the battle royal that takes place between hacker-turned-rebel-hero Neo (Keanu Reeves) and a courtyard full of clones of Agent Smith (Hugo Weaving), the computer application/enforcer whose mission it is to keep human beings from unplugging themselves from the titular Matrix, the illusionistic computer program that keeps them enslaved.

The second is a protracted freeway car chase in which futuristic guerrilla warriors Morpheus (Laurence Fishburne) and Trinity (Carrie-Anne Moss) try to prevent an old man called the Keymaker (Randall Duk Kim) from falling back into the clutches of Merovingian (Lambert Wilson), a French-speaking scoundrel who is also somehow involved in the upkeep of the Matrix.

Taking place to large extent on the roof of a barreling 18-wheeler, this eye-popping, heart-stopping scene also involves pursuit by Merovingian’s henchmen, a pair of pasty-faced, white-dreadlocked hunks known as the Twins (Adrian and Neil Rayment).Why white dreads? Because, like everything else in this movie, it simply looks cool.

When the episode of nail-biting finally ends, not with a bang but with an even-bigger bang (facilitated by the 11th-hour arrival of Neo, a deus ex machina in designer shades), I could have gone home happy. But the movie was nowhere near over.

Even later, when it was over, it was nowhere near over.

Does Neo ever get acknowledged as “The One,” the Messiah-like figure whom the rebels attempting to throw off the shackles of the Matrix have been hoping for? And what of the prophecy that Morpheus keeps referring to, the one foretelling the end to their armed struggle?

For the answer to these and other burning questions–such as, “What the heck is that weird-looking robot thing briefly glimpsed in the rebel stronghold of Zion?”–you’ll have to stay tuned for Part III.

It’s a canny marketing strategy, ensuring that everyone who sees this movie (and that likely includes everyone who saw the first one, plus his little brother) will have to come back again just to figure out what in heaven’s name is going on.

So is the new movie confusing? You might say that, with a script so larded with talk of causality, choice and destiny, it sounds at times like my old notes from Philosophy 101. I think I’ll put my order in now for the DVD version of “Reloaded,” just so someday I can play back the conversation between Neo and the Architect (Helmut Bakaitis, looking like a cross between God and Donald Sutherland).

Over the course of several paragraphs of computerese, philoso-babble and “The Prisoner”-style surrealism, the man who designed the Matrix expounds on What It All Means and Why, and How It All Boils Down to Picking One of Two Doors. (What is this, “Let’s Make a Deal”?) Needless to say, the tension, along with everything else except sense, has been ratcheted up until it hurts.

Fortunately, sense doesn’t really matter. “The Matrix Reloaded” is about sensation, not logic. As such it delivers, in spades, exactly what you should expect from a popcorn flick–thrills, chills and spills–plus a little more for good measure, just to keep anyone who might want a beginning, a middle and an end from whining.

“The Matrix Reloaded” (R, 138 minutes) contains extreme martial-arts violence and gunplay, sexuality and some crude language and opened last week.