For me, the appeal is the gritty and dark atmosphere that is incredibly consistent throughout the entire album. RZA's got some incredible beats, between the trumpets on Living in the World Today, that crazy guitar sound at the beginning of 4th Chamber, and how the bass works so well with the violins on Investigative Reports. It's seriously one of RZA's best works in terms of production, if you liked the raw sound of 36 Chambers this should click right away.
As for the lyrics, like I said before, GZA's one of the strongest lyricists in the Clan (like, at least top 3). The imagery he's capable of and the multi-syllable rhymes on nearly every other bar, delivered casually and effortlessly, make him stand out to me as a rapper. I really don't view him as boring or low energy at all, to me he radiates confidence on every verse he does, in a similar way Method Man does-he's making it look easy to rap like that.