LONG A POLARIZING figure on the underground scene, Talib Kweli was the “next big thing” for what seemed like years and years until, suddenly, he wasn’t.

A man whose reputation for melding socially conscious subject matter with mainstream exposure precedes him, Kweli has been dogged by numerous failures and shortcomings since his emergence as a solo artist in 2002, following his excellent collaboration albums with fellow Brooklynite Mos Def (Black Star) and producer Hi-Tek (Reflection Eternal).

The reasons for this stagnation are many, some of which have been rectified for his latest record, and some of which seem unshakable curses.

His fourth solo release, “Eardrum,” finds Kweli back in his musical comfort zone — a myriad of neo-backpacker producers, who count Kanye West, will.i.am, and old buddy Hi-Tek among their number, have constructed a pleasing if conventional soul- and jazz-infused street poetry soundscape for our MC to explore.

Talib has spent the greater part of the last six or seven years trying to infuse his aggressively empowerment-obsessed rhymes with an accessible, mainstream sound that save for a handful of strong tracks have fallen flat both musically and commercially.

His 2004 follow-up to the ironically mistitled “Quality,” entitled “The Beautiful Struggle,” remains the apex of his immense ignorance regarding the effective way to bring strong, positive, and, most importantly, sophisticated messages to the forefront of rap. His beats were generic sub-Kanye backpacker drivel, and his MCing, well, we’ll get to that later.

The beats this time around, while hardly a revelation, have an air of belonging, bringing Kweli closer both to the music to which he raps and to the lost era before the squandering of his arguable potential. The smooth, soulful production on subtler tracks like “Country Cousins” (featuring song-stealing verses from Houston rap duo UGK), “Holy Moly,” and Norah Jones collaboration “Soon the New Day” remain the highlights of the album after numerous listens, while the more abrasive, self-important backing tracks of “Hostile Gospel Pt. 1” and “Say Something” provide a harrowing backdrop that alone sounds great but ends up seeming over-the-top when coupled with Kweli’s socially conscious preaching.

The question becomes, how can the truly great hip-hop artists like Nas and his heir apparent, Lupe Fiasco, pull off didactic, diverse subject matter while still crafting musically original and sonically complex final products? On paper, Talib Kweli has been one of the top five lyricists in the rap game since his introduction to the underground scene in the mid-'90s, but has never in his life been within a mile of the 20 best overall MCs.

A lot of slack has been cut for Kweli in the name of supporting “real hip-hop,” but at what point does it become destructive to give props to a man who possesses not a fifth of the performance artistry of his contemporaries at the forefront of the underground scene?

His awkward, rigid flow is disruptive to the aesthetic of his music, upsetting the rhythm and barring even the most quality beats from translating into truly listenable songs. Nas, Ghostface, Jay-Z, GZA, and their contemporaries came up in a time when smart writers were a dime a dozen, and as such had to possess a strong sense of rhythm and verbal dexterity that Talib Kweli simply lacks.

It is this lack of musical artistry in conjunction with Kweli’s raw lyricism that is the gargantuan obstacle in fully enjoying his output. Either he doesn’t realize it, or he thinks it’s not important, but the truth is that it on several occasions makes a track whose deft worldplay and intensity of subject matter physically knock the wind out of you seem trite and saccharine. Even at the lyrical apex of “Eardrum,” the KRS-One collaboration “The Perfect Beat,” Kweli sounds frantic and offbeat in a way more reminiscent of really fast talking than the forceful, charismatically offbeat musings of The RZA or Ras Kass.

While Kweli has admirably taken steps in his beat-selection process to ensure that he is immersed in a more underground soundscape rather than removing himself from his comfort zone and rapping over more mainstream music, much of the veteran Brooklyn MC’s shortcomings either have not been or cannot be rectified, once more barring his record from being sonically innovative and intensely original as well as didactic.

Sadly, until he takes some notes from his buddies Common and Black Thought on incorporating musical considerations into his writing process, he will remain the best rapper alive who can’t rap.