DG has gathered on this convenient 9 CD set, all the Beethoven Sonatas recorded for them by Emil Gilels in his later years. He died, in 1985, shortly before his 69th birthday, before he could complete the cycle. They were originally published as recorded, over more than a decade, between 1972 (Sonatas No.21 "Waldstein" and 28 op. 101 - Gilels was 55 then) and 1985 (three releases then: the two so-called "Electoral" Sonatas WoO 47/1 & 2, here on CD 1, paired with No.11 op 22; No.5 op. 10/1, No.10 op. 14/2 and 19 op. 49/1; and finally No. 30 op. 109 & 31 op. 110). Some of those originally released on LP were also previously reissued on CD, but in reshuffled couplings, sometimes even duplicating each other (as the 1972 Waldstein, the 1973 Appassionata and the 1974 "Les Adieux", Beethoven: Sonataen - Waldstein, Les Adieux, Appassionata, or the same Appassionata with the Pathétique from 1980 and # 31 from 1985 (haven't found an entry on this website, it is listed under ASIN B0002UJJCS on the European sister companies, part of the Penguin Rosette collection), or again the pairing of 27 from 1974, 28 from 1972, 30 & 31, Beethoven: Klaviersonaten Nos. 27, 28, 30 & 31 [Germany]). Some others from the LP era were reissued only in the previous box set collating all of these recordings (Beethoven: 29 Piano Sonatas / Gilels - not an entirely honest title, as there are 29 Sonatas there only by dint of including the two early sonatas without opus number) and never made it on individual CDs, at least on DG (the whole series was licensed by Olympia and released on individual CDs) : No. 6 op. 10/2, 12 op. 26, 16 op. 31/1, 25 op. 79.
As the other reviewers have noted, the sound is uniformly good, and I don't hear any significant differences between the earlier and the later recordings - maybe slightly more vivid presence in these (and, over headphones, the occasional rumble of cars in the distance).
The liner notes contain only an interesting general presentation of Gilels and Beethoven, but no analyses or presentations of the sonatas themselves. I'm particularly happy to have the two (out of three) early and obscure "Electoral" Sonatas from 1783 - nothing to do with democracy, they were dedicated to the Kurfürst or Archbishop-Elector of Cologne Maximilian Francis von Habsburg-Lothringen: they were in fact Beethoven's first piano Sonatas and I find their Haydn-esque wit and Sturm-und-Drang atmosphere irresistible. The essay contained in the liner notes is also very imprecise about which Sonatas Gilels didn't live long enough to record: they are No. 1 op. 2/1, 9 op. 14/1, 22 op. 54, 24 op. 74 "A Thérèse" and the ultimate one, 32 op. 111. An irretrievable loss: there are no other recordings, studio or live, of any of these Sonatas in Gilels' discography (the website of the label DOREMI hosts a magnificent Gilels discography compiled by Ates Tanin, to which I am entirely indebted for this review).
For this reason only, this set obviously cannot be recommended as your only set of complete Beethoven Sonatas. As to the point of determining whether those we have are "the best" versions, it is a pretty senseless one, I think: ever since the advent of the recording process, there have been numerous complete recordings by the greatest giants of the piano in the 20th Century (starting with Schnabel, Backhaus and you name `em). And that's not mentioning those giants who have not recorded the complete cycle but only samples (Richter comes to mind, of course). Suffice to say that Gilels is one of these giants. No one seriously interested in the Beethoven Sonatas should fail to listen to him.
Yet beware: as I write, the demanded price on the present website seems abnormally high. It sells for significantly less on the European sister companies, and I personally bought my own set on the famous Internet auction site for less than 20 $, postage included.