First the contents: this set includes Zubin Mehta's Symphonie fantastique with the NYPO, Sir Colin Davis' Harold in Italy with Nobuko Imai and the LSO (originally on Philips), Lorin Maazel's Requiem, Davis' Tristia (from same Philips rec. as Harold), Charles Dutoit's rednderings of eight overtures, and his magnificent reading of the Symphonie funebre et triompahle with the Orch. Sym. de Montreal. The rest are tidbits: Norrington conducting some very rare Berlioz choral works, such as "Le Temple Universel" and "Tantum ergo." There's even two performances of the Prelude to Les Troyens a Carthage (Dutoit for one, Davis for the other).
So, it's not exactly "the essential masterpieces" as the box says. I could write a whole 'nother review of what they could have left off, and how they could have better-presented the works. To make just one suggestion: rather than have a CD devoted to overtures, why not spread the most famous ones out and pair them with i.e. the Sym. Fan., or Harold? That makes a bit of room for one more disc of opera highlights, or something.
Now for the music and performances: this is a mixed bag, if you really care about Berlioz as I do. For a beginner (which is the aimed-at audience, I gather) it's fine. Mehta's Symphony flows along just fine in most places, but really misses the heart and drama of the piece. Davis' Harold and Tristia (almost sounds like the name of a novel) are very good, and the only weak spot is the Funeral March for Hamlet (#3 of Tristia). Maazel's Requiem is frustrating. On one hand you have superb (really superb) choral singing. On the other hand you have anemic orchestral playing and direction. Maazel underplays/downplays/suffocates the big brass outburst in the Dies Irae. That's a major nono, in my book. It so happens that Berlioz loved that moment and he wrote ecstatically about that one moment of "utter chaos." Moving on, we come to Dutoit's two big contributions: the Overtures and the Funeral and Triumphal Symphony. The whole chemistry of Berlioz+Dutoit+l'Orchestre Montreal=music-making of the best kind. Those performances alone made the purchase worth it.
Finally, the tidbits: they're interesting, but not representative of Berlioz at his best. Or even at his obscure best. But they are rare, and enjoyable, and if you care about obscure Berlioz works as I do, they are a very nice bonus.
EDIT: One last thing. There are no liner notes. The set is cheaply done, thus the cheap price. But it's a great bargain nevertheless. And who needs liner notes when you have the Berlioz Memoirs?!