This recording has received 'rave' reviews in both Gramophone (July 2004) and BBC Music Magazine (October 2004), and I refer you to these for 'expert' opinion, which mine is not.
No one who loves this monumental work will be satisfied with just one disc, and as readers of the Penguin Guide will know, there are many excellent recordings to choose from.
Why chose Harnoncourt? He comes with a certain reputation for stamping his personality on the works he conducts, which is not to everyone's taste.
But what he does do, especially in Mozart, is get away from a certain 'plush' 19th Century romanticism, which for me takes away the raw, elemental grandeur of works like the Requiem and the Great C Minor Mass.
Conducting the Concentus Musicus Wien, with a fine team of soloists, and backed by a superb recording, this should disc be at/near the top of any buyer's shortlist.
As a bonus, Harnoncourt writes his own notes, in which I found much that was new to me about the background, genesis, and 'completion' of what he calls Sussmayr's "stopgap solution".
In fact, what he uses here is "the new critical edition by Franz Beyer, which carefully corrects technical mistakes made by Sussmayr" but no more than that.
I would like to award six stars, but Amazon won't let me!