The preview includes the Introduction, The Planet Trillaphon as It Stands in Relation to the Bad Thing, Kevin Dettmar's afterword, excerpts from The Broom of the System, and Gerald Howard's afterword.
I received a couple of copies in the post today for my tiny involvement in this collection (I was asked to write the afterword for Incarnations of Burned Children) and now I truly understand that commonly expressed feeling of not wanting to look at something one has written, ever again, now that it is an actual... thing.
Putting all that behind me it's an extensive collection that, yes, contains excerpts of the long things, but also contains Wallace's very best short fiction, non-fiction, and teaching materials. I've not read all of the afterwords, but those I have managed to get to this evening make me want to take my time with the rest.
The newly collected passages from Wallace in the selected teaching materials (beautifully introduced by Sally Foster Wallace) highlight his passion for teaching that I know many of his readers wish they were able to experience first hand. There is certainly material in here that will inform my teaching in the future.
[This is where I usually hit you up with a pre-order link to Amazon US because the small commission helps me keep this site running. Unfortunately, the link just takes you to the page where you'll be able to the buy the book when it is released on Nov 11 (thanks to that ongoing dispute). I still haven't decided what to do about it yet...]