In Utero is much like the Pixies Surfer Rosa, in which Steve Albini's production (or recording) increases the impact of the material, what would Rape Me or Tourettes sound like with out the skinned face production?
In Nevermind the guitars had a sort of glossy heavy metal sheen to them, that was part of its appeal, but when the first roar of a guitar (is it a guitar? it could be a musical vacum-cleaner) is heard, the album is downright heavy.
While in Nevermind the drums carried the song, it was more in a top 40 way, in In Utero Albini's production has the trademark loud mid-rangey sound, and indeed they carry the song much better than ever in Nevermind, the un-comprimising sound of the drums really show how great a drumer David Grohl is, in Nevermind they were hidden, but here they're in full veiw without any sheen.
With the non-production of In Utero the quiet parts are quieter and the loud parts are louder, and the effect heavys the album, combined with Kurt Cobain's suicide note lyrics the album is the defening roar of a tourtered mind.
It really is the best Nirvana album avalible, unlike Neverminds candy sheen, Bleachs grunge heaviness, In Utero is the best of all worlds, amazing.