By now I'm sure you've perused the track list for the Big Star box set (link to Amazon below if you haven't – they're also starting to lower the price for pre-orders). What's my take? I'll be thrilled to get it. My only concern before hearing it (CAVEAT! PLEASE NOTE! I'm not one of those obsessive fans who freaks out and criticizes a recording / movie / whatever before they see or hear it. This is just idle musing for entertainment purposes. Got it?) the use of alternate mixes for some of the tracks for #1 and RC to the exclusion of the LP versions (it appears that 3rd is presented intact). There's an assumption made that you have the original recordings (and I'm sure that few who buy the box set won't have the originals). But knowing at least some of the people involved, I'm sure there was good reason for the way things were done. I'll probably just load all the discs into my Mac and then make discs that edit out all the original versions, not wanting to mess with the perfection of the original discs in my head. Even if the alternate mixes are better (who knows? they might be...) I'll still want to hear them separately rather than in the flow of the album.
As I've noted before, Big Star fans are going to freak when they hear Alex's acoustic demoes for Life Is White and What's Going Ahn. The only track not on the box that I would have lobbied to include would be an instrumental track for September Gurls without the vocals. It's an absolutely stunning testament to the band as creative musicians and John Fry as a brilliant engineer. Maybe a little too "inside" for some, but for anybody who's ever been in a band, it would be revelatory. A textbook example of how it's done...

