The use of a counter-tenor for alto parts is as close to original Bach as we can get nowadays. Bach would have used male voices in his choirs, but these would have been adolescents, whose voices broke much later in those days, not men singing in a trained falsetto. We are therefore seeking to reproduce a sound that can no longer be reproduced. I personally have nothing against female soloists in Bach; indeed, I have a very nice recording of Dame Janet Baker singing Bach, including BWV82. However, a good counter-tenor is also worth a listen.
Andreas Scholl is such a counter-tenor. Not only does he sing beautifully, but he also has a clear grasp of what he is trying to achieve, and of the profundity of Bach's music. The highlight here is the wonderful BWV82 "Ich habe genug", with the meltingly beautiful and moving aria "Schlummert ein". I'm not sure what it is about the story of Simeon and the child Jesus that brings out the best in composers, but it is also the highlight of Rachmaninov's Vespers. There is also BWV169, with its famous sinfonia, plus other arias from various Bach cantatas, plus BWV53, which was once attributed to Bach, but which is now known to be by Georg Melchior Hoffmann.
I have three full cantata sets, but this is a worthy addition to them.