In the hip-hop business, success is a strange beast — a “sick cess,” as Tupac once said. On “The Massacre,” the tastelessly-titled new album by hip-hop scion 50 Cent, the extravagant success of the rapper’s debut rears its ugly head, dimming what should have been an accomplished sophomore effort. It’s not particularly awful — of course, 50 easily trumps countless leagues of two-bit rappers out there — but it’s neither an exciting pop album nor a work of hip-hop genius.

50 Cent stands chiseled and erect on the CD cover, his Nubian-warrior muscles bulging like swollen balloons, a striking image of vitality that should echo throughout the album. But if becoming a millionaire hasn’t affected the rapper’s exercise regimen, it’s certainly tempered his once-dynamic flow. He seems to spend most of “The Massacre” simply trying to wriggle out from under the long shadow cast by his record-breaking debut, “Get Rich or Die Trying.” Of course, no one expected him to match the success of the Dr. Dre-produced “In Da Club” — with its stadium-sized bass exploding under exquisitely timed vocals, at once both brassy and sensuous, it ranks among the most perfect hip-hop hits. Yet the gulf between that peak and “The Massacre” is too vast to ignore — 50 Cent vainly struggles to recapture the mojo of his inaugural number. But for all the cheeky lyrics of “Disco Inferno” and the deep-throated purrs of “Candy Shop,” one still pines for that mother of all high-school dance sing-alongs: “Go shorty/ It’s your birfday…”

The closest 50 comes to an “In Da Club” is the booty-smacking “Disco Inferno,” a hotbed of slapping drums and hypnotic hand-claps. The rapper injects just enough energy into his catchy rhymes to keep the club hounds singing along, but the song as a whole can’t strike the right balance between revival and rip-off. Right away, he begins with the instantly-recognizable “Go, Go, Go” of “Club,” yet soon reminds us that “Y’all already know what I’m about” and lets things mellow out from there. A line like “Next level now/ Turn it up a notch” is ironically dead on this almost-there number.

On its own merit, though, “The Massacre” is a polished piece of work, a showcase of some of the best beats money can buy. The Eminem-produced “Gatman and Robin” is an auditory apoplexy, a bursting, convulsing number that viciously pops twitching violins under a flourishing electric guitar and other seizure-inducing sound effects. Likewise, the slasher-flick-themed “Piggy Bank” screeches an ominous violin under night-of-the-living-dead shrieks. 50 Cent does his best zombie impression on the spooky chorus, lusting for cash like a monster lusting for flesh. “Clickity clank/ Clickity clank/ The money goes into my piggy bank,” he sings eerily.

Like his protege-turned-malcontent The Game — whom he recently agreed to make up with at a charity event, a wise and generous decision — the public persona of 50 Cent is a vehicle for his talented, dexterous producers. A conspicuous standout is Scott Storch, whose simple but sumptuous beats recall some of Dr. Dre’s best work, yet retain the energy and freshness of an up-and-coming hitmaker (not to mention his “Tuff Jew” moniker that stands out in the liner notes). With its swirling flutes and buzzing violins, the Storch production “Candy Shop” is exotic and sexy, yet hard-edged enough for the streets and the clubs. On “Just a Lil’ Bit,” Storch skillfully juxtaposes a delicate confection of whistling piccolos and shimmering sitars against a heavy drum beat thrusting underneath. If nothing else, it provides innovation for an album — and music industry — that is largely stagnant.

Interestingly enough, Dr. Dre maintains a frosty distance from the CD, appearing only as executive producer, mixer or assistant producer on a few tracks. For all the snappy gumption of the younger beatmakers, the album longs for a Dre-helmed sensation, something that can excite 50 Cent’s world-weary ways beyond the listless, placid flow he brings to most of the album. As he brags on “Candy Shop,” “I’m a seasoned vet when it comes to this s**t,” as though the incredible success of his debut has already jaded him to the thrill and elation of it all. Sure, the album is chock full of number-one hits, but even a smash like “Candy Shop” feels oddly lifeless, with its staccato “whoa”s and “uh huh”s that sound more like a foot massage than hot sex.

Despite the mediocrity of his verses throughout the album, on “Gatman and Robin” 50 Cent competently keeps up with one of the wildest beats Eminem has ever concocted. And while his thuggish lyrics are certainly aggressive enough — “I’ll be actin’ like an animal, I’ll tear you apart/ If the masterpiece was murder, I’d major in art” — they just don’t quite hit the nerve like they should, and have little else to say besides empty self-promotion.

Maybe his gigantic balloon muscles on the album’s cover really are a reflection of the CD as a whole — an intimidating veneer, but underneath it’s really just a bunch of hot air.