This is a very good boxed set, especially for those who don't have any Cream CD's, as it has all the albums, plus a little bit more. The reason it doesn't have a whole lot of unreleased tracks is that the Atlantic tape library burned down in the early 70's, and that included all the acts who recorded for the label up until 1969, and so all that remains for a lot of Atlantic/Atco bands (including Cream) are just mixed-down master tapes for LP's and singles. Any unreleased cuts from, say, "Wheels Of Fire" or other live shows recorded for the live albums are gone.
The "Disraeli Gears" rehearsals are fascinating, though, but it would have been equally wonderful to have some outtakes from the "Fresh Cream" sessions (which are out on bootleg, and have excellent sound quality). I have to say, the live version of "N.S.U." on here is no match for the version found on "Live Cream", and it sounds like some of the live cuts from "Goodbye" that appear here have different mixes. I like how the live tracks all seem to flow together, like one whole show.
For some of the live cuts that aren't on here, like "We're Going Wrong", check out the "Fresh Live Cream" video, as it's excellent. A mono vinyl pressing of "Fresh Cream" is also well worth looking for, as it's a little thicker sounding, and a lot less echoey than the stereo mix that we all know and grind our teeth at.
So, all in all, the boxed set is very good, but don't expect a whole lot of surprises, though it's not without a few of them.