I am a little more inclined to celebrate "well played" discs, but in this case, the musical virtues go further than simply accurate reproduction of the notes.
The BSO may have peaked in terms of distinctive interpretations and stylishness under Monteux, and Munch, but the refinement of the playing under Ozawa was often extraordinary. The DG engineering and pressings, the Symphony Hall sound, many excellent guest conductors and soloists, and yes, even Ozawa's keen ear for color, meant the 1970s were another kind of peak.
I know many Bostonians were disappointed with the direction the orchestra took, but the recordings (and the broadcasts) were world-class in many respects. For those of us who admire the legendary principal winds of the BSO during the 70s, the set includes some irreplaceable classics.
So my take on this set is a bit different than yours. Anyone who loves orchestral playing will find much to cherish in this set; anyone who is interested in the repertoire will find many delights. I count at least 50 discs that are exemplary--or at least have an uncontested place on my shelves. There are others that are excellent enough to transcend these cheap per-disc prices.
Abbado's vivid Poem of Ecstasy plus excellent Debussy
MTT's Tchaikovsky 1, Stravinsky, Debussy, Ruggles, and Ives (all near top choices)
Steinberg's Strauss, Hindemith, and Holst (all superb)
Kubelik's Smetana and Bartok (plenty of authority in both)
Jochum's Schubert/Mozart (big band but beautiful)
Ozawa's Berlioz (especially the Symphonie Fantastique, but the longer works are also very well done), Respighi (as noted by others, a great pair of discs), Ives, Poulenc, Mendelssohn (exquisite), Faure, Ravel (an all-round fine set), and Prokofiev and Tchaikovsky ballets (seriously, the Swan Lake is a must, the others are superb)
concerti with Wright (essential), Walt, Eschenbach (a sleeper), Mutter, Rostropovich, Zimermann, Kremer, Shaham
Bernstein's Liszt (long a first choice for many)
Throw in the very attractive Nelsons recordings from a different era entirely, plus the BSO Chamber Players.
I suppose Ozawa's Chabrier, his Brahms 1 or Mahler 1 don't actually rise to the level of top-rank, but actually these are quite good too and well worth having if you're a fan of the orchestra.
I have not heard the previously unreleased Brahms 2 and Rossini Semiramide Overture, which should be icing on an already rich cake. Everybody has their own calculus, but I can't fault anyone for wanting this set.
--Jeff