After listening to a recent BBC 'composer of the week' podcast about Schuman, I am instantly interested to explore his work. The excerpts of the works they included sounded brilliant.
So, am considering:
Would also like to buy a recording of the violin concerto.
Of course, this is all for when I actually have some money! 
Oh, Daniel there's a lot to enjoy there for sure. Schuman is certainly a fascinating composer. I don't own this box but do own all the individual releases and bought them all in one foul swoop last year. I really need to go back and listen to the music because there was some of it that didn't register with me the first time around. I did like
Symphonies 3-5, 8 but I don't remember the other ones too good. The reason why
Symphonies 1 & 2 aren't in the box is because the composer withdrew them. I'd love to hear them though.
P.S. Daniel, I urge you to go to the William Schuman thread on the Composer Discussion section of the forum. I'm sure you'll find some fun information about the composer and will get the opinion of his music from other GMGers.