The coolest part about “Kingdom Come” is the case it comes in. It’s made out of some kind of special material. When you take the CD booklet out, the picture of Jay-Z’s head goes from not having a hat to having a hat and sunglasses. It’s so cool. But that’s the best part of the album. The rest is just evidence that Jay-Z should have stayed in retirement.

“Kingdom Come” should be a great CD. Producers include Kanye West, The Neptunes, Dr. Dre and Just Blaze. The album features collaborations with John Legend, Beyonce, Ne-Yo and Usher. Leading Man: Jay-Z, aka Jigga, aka Young Hov, aka H.O.V.A., aka the hip-hop giant who has made more hits than any other rapper. Ever.

But this album is flaccid like Dr. Dre’s stomach; totally unexciting, especially once the thrill of the CD case wears off. The hour-long disc doesn’t present a single memorable hook. Instead, listeners get songs like “Show Me What U Got,” the album’s single. “Show Me What U Got” is a Just Blaze production that tries to sound like Kanye West’s “Touch the Sky,” but it fails because the looping track that Jay rhymes over is too muddled. It features a repeating drum break and complicated crash part that is overly complex for the simple vocal rhythms Jay haphazardly throws over them, and the end result is that the rapper’s normally loose flow comes off as completely offbeat every time the drum break starts.

Perhaps Just Blaze was trying to push the boundaries of his genre. Perhaps he was trying to expand our idea of what “single” should be. But he didn’t. Instead, he forgot to entertain his listeners, most of whom will probably stop “Show Me What U Got” to go listen to “Laffy Taffy” instead.

The flaws of “Show Me What U Got” continue throughout “Kingdom Come.” The cast of all-star producers eventually delivers a few good tracks, but they never sync up with Jay’s unique style to create something special. The only exception is the album’s title track, “Kingdom Come.” Its thick layering of instrumental tracks creates the perfect backdrop for Jigga to drop rhymes about how he’s superman. Still, it’s in this song that Jay claims, “I’m so evolved, I’m so involved / I’m showin’ growth, I’m so in charge.” The rest of the album only contradicts this statement, indicating that the Jigga Man might actually be regressing.

This backward trend is especially evident in the album’s collaboration tracks. There’s always an element of risk involved when rappers and vocalists work together. When successful, such collaborations can lead to club-bangin’ classics like Ludacris and Usher’s “Yeah!” or Big Boi and Sleepy Brown’s “I Like the Way You Move.” When they fail, however, listeners might be subjected to something like Ja Rule and Vita’s “Put it On Me.” Luckily, none of the collaborations on “Kingdom Come” are that bad, but none of them achieve anything beyond mediocrity either. This is a definite step down from Jay-Z’s past collaborative works with Biggy Smalls and The Roots band.

Jay-Z should have rested on his laurels, as “Kingdom Come” only dilutes the great body of work he left behind when he quit the rap game back in 2004. Remember that Jay-Z once set the standard for great pop rap? This is the hit-maker who gave the world “Big Pimpin.’” This is the artist who took the melody from “It’s a Hard Knock Life,” a song from the Broadway musical “Annie,” and somehow made it into a dope hip-hop riff. This is not an artist we would expect to make an album like “Kingdom Come,” a work that does not even come close to standing up to such past Jigga masterpieces as “Reasonable Doubt” and “The Blueprint.”

Still, when you need Jay-Z, you need Jay-Z. If you’re currently craving some of Young Hov’s lyrical styling, go buy the often-overlooked “MTV Unplugged: Jay-Z (Live).” It’s a live recording of a concert that Jay did for MTV’s “Unplugged” series, and it features The Roots band and Jaguar Wright. It’s amazing, highlighting all of Jay’s strengths as a lyricist and as a performer that are absent from “Kingdom Come.” Just leave the CEO of rap’s latest album in the New Releases section and wait until Jay comes out with something worthy of his own greatness.

Kingdom Come

Jay-Z

Roc-A-Fella Records