First, a given: this is a fantastic set of classic music and performances.
I think the mastering is technically superb, and though some will decry that the engineers left the masters original and did not correct channel placement "errors" (if you even want to call them that), I think the Quad mix is great, especially remembering the vintage of these tracks, the earliest of which dates to 1967 and was NOT recorded in the New York studios but in Memphis, in a much more technically limited environment.
Song selection? "Greatest" is arguable, but at the end of the day most of the big stuff is here. I would love to hear lesser-known classics such as "Young, Gifted and Black" with its big vocal chorus and "Since You've Been Gone" in MC, but I'm more than satisfied with what this album represents, and kudos to Rhino for doing a great job with the mastering and packaging.
I agree that it sounds better than the Q4 conversion, but that's not a knock on the convertor - Rhino has the masters, whereas even the best commercial Quad reel source is still a low-speed consumer-level dub generations removed.
I do think it's a bit odd that the default audio stream is Dolby Digital when the DTS is so clearly superior, but that's a niggle and does not detract from the overall package. Nice job, and I'm very glad to have it!