Recently at work, I listened to both Nevermind and In Utero. While Nevermind is not a bad album at all, In Utero COMPLETELY blows it away, in terms of lyrics, song structures, etc.
I hate to use the tired cliche, but Kurt really wore his heart on his sleeve for that album. It really is all over the place, from the catchy, almost pop-grunge of "Serve the Servants" to the straight up metal riff that is "Scentless Apprentice" to the rather sullen "Pennyroyal Tea." I really can't find too much fault with the album at all. It's produced perfectly, sounding just as raw as every lyric Kurt wrote. In Utero is just a tremendous album overall, blowing away everything in their catalogue as far as studio albums go.