I am a bit of a Steve Albinin fanboy. I never miss Shellac when they come to town and I will always give an album he recorded more of a serious listen than if he wasn't involved.
I'm no much of a Nirvana fan anymore and this letter really doesn't say much about Nirvana at all. http://en.wikipedia.org/wiki/In_Utero_%28album%29 has some interesting background about the album, which they gave to remix masters in the end anyway.
I liked, but didn't love In Utero. I would love to hear the original mix. Something about the album feels chunky, like it doesn't venture to any extremes. I think Nevermind actually captured a real essence of Nirvana, a smart co-opting of pop music. It wants to come through in In Utero (rape me), but something is holding it back. Even Bleach feels more pop than In Utero.