After his bizarrely cartoonish turn in House of Gucci, it’s a relief to see Jared Leto channel his lust for transformative characters into a film where that’s quite literally written into the role’s DNA. He plays the title figure in Morbius, known as “The Living Vampire” in the Marvel comics from whence he hails. Leto gets to juggle time as the brilliant Dr. Michael Morbius — who has spent his life searching for a cure for the rare fatal blood disease that afflicts him — with the blood-sucking monster he becomes, which fills his soul with horror.

After a promising start, Daniel Espinosa’s long-delayed film only intermittently matches the intensity of the lead performance, and the script by Matt Sazama and Burk Sharpless becomes thin on story, choppily stringing together chaotic outbursts and action clashes that build to a painstakingly foreshadowed “sibling” face-off. None of that seems likely to deter the geek faithful, even if this new entry in Sony’s Spider-Man Universe often seems a lot like a boilerplate Venom installment, without the humor.

A tense prologue takes place in Cerro de la Muerte in the misty mountains of Costa Rica, where a frail, emaciated Michael hobbles from a helicopter on crutches into the mouth of a cave that’s home to thousands of vampire bats. While the chopper pilot frets about getting out of there before dark, Michael spots a half-devoured animal carcass and notes admiringly that while the bats weigh almost nothing, they can overpower a creature almost ten times their size. Without warning, he slashes open his hand to serve as bait.

Cut to 25 years earlier in Greece, where the young Michael (Charlie Shotwell) is in a clinic under the care of Dr. Nicholas (Jared Harris) when he meets new patient Lucien (Joseph Esson), a British boy roughly the same age and with the same blood disorder. They bond instantly, with Michael giving his new friend the nickname Milo and likening the two of them to the Spartans: “We are the few against the many.” Which is the only semi-discernible reason for this part to take place in Greece.

Back in the story’s present in New York, Michael has become a renowned doctor, who shocks his trusted colleague, Dr. Martine Bancroft (Adria Arjona), when he turns down the Nobel Prize for his development of artificial blood. That’s just the beginning of his work, Michael explains, which is where the “aquarium” — actually a massive upright cylindrical glass chamber — full of bats brought home from Costa Rica comes in.

Both Michael and Milo (Matt Smith) continue to be treated by the weirdly ageless mentor figure of Dr. Nicholas. Milo, meanwhile, has inherited a fortune, so he’s bankrolling Michael’s lab experimentation while hungrily soaking up whatever life he can in his louche, playboy style, as his body continues to deteriorate.

Given that the procedure of mixing human and bat DNA is considered both unethical and illegal, the first trial has to be done in international waters off the Eastern Seaboard, on a cargo boat manned by shady mercenaries. Martine injects the serum into Michael’s spine, and while we don’t witness the actual transformation, we definitely see the end result spring into action, which is bad news for the crew.

The upside is that it gives Michael Olympian athletic prowess, superhuman strength and exceptional sonic radar. Oh, and springboard skills that soon morph into the power of flight. The downside is creepy bat eyes, a gnarly manicure, fangs and a thirst for human blood that needs to be sated whenever the serum wears off.

The movie from there on out is basically Michael wrestling with his conscience, vowing that what happened on the boat can never happen again, while FBI agents Stroud (Tyrese Gibson) and Ramirez (Al Madrigal) investigate the string of violent deaths that begins there, with corpses mysteriously drained of blood.

The body count is destined to keep climbing when Milo gets his hands on the serum and reveals fewer scruples about his new favorite tipple. “All our lives we’ve lived with death hanging over us,” he tells Michael. “Why shouldn’t they know what it feels like for a change?” Besides, the bat transformation of Milo’s face when he’s on the juice does wonders for Smith’s cut-glass cheekbones. But the different views of Michael and Milo toward suppertime inevitably will set brother against brother, with Martine at risk in between.

While DP Oliver Wood shoots most of the action with the lugubrious palette that’s become standard for this end of the Marvel spectrum, he makes atmospheric use of New York’s subways and underground spaces in several scenes. The thundering score by Jon Ekstrand, with its pounding percussion elements, also pumps up the energy, even as the plot slides into repetitive grooves.

The look gets a boost from the effects team’s visualizing of sound waves received by Michael and Milo whenever they’re in vampiric mode, bouncing off people, objects and buildings in their paths. Their speedy movements are also trailed by a dusting of color; that’s never really explained, but it looks cool, especially when Michael’s in an orange prison jumpsuit or a flapping black coat with bright purple lining. Their facial transformations are entirely digital, done without prosthetics, effectively straddling the divide between photorealism and comics.

But like so many movies rooted in comics, much of Morbius seems like groundwork for more complex storytelling to come, and especially for crossover chapters, one of which is set up in two mid-credit sequences involving a character (and star) seen previously in Spider-Man: Homecoming.

It’s just a shame this opening salvo takes itself too seriously to have much fun with the mayhem, despite the potential in Smith’s devilish turn for amusing interplay between the antagonists. Arjona carries herself with confidence but her character also gets a little lost in the carnage; perhaps the late-breaking romance between Martine and Michael will acquire more of a heartbeat in the next round. Leto certainly broods up a storm behind his veil of rock-star hair, but the movie has too little to distinguish it from the second-tier (or maybe third?) Marvel pack, ending up as more of the same.