This whole argument of piano vs harpsichord seems to rear its ugly head very often and especially when it comes to Bach's keyboard works. The Well-Tempered Clavier is not immune to this. I must admit that it always disturbs me when I come to buy Bach's keyboard music. There is always this nagging voice in my head that says that the piano is not a baroque instrument and the spirit of Bach's music is lost. I do not know how I am going to get around this or if I ever can. I find that Gustav Leonhart's harpsichord recording of the Well Tempered Clavier as baroque as one can get and as close to the spirit of these works as one can get. Finally I would like to add that I do not have any recording of Bach's keyboard works on piano-not even the illustrious Glen Gould recordings of the Goldberg Variations on piano.
Well, I'm sure this argument has been had on here a 100 times (maybe less, maybe more), but I vastly prefer the piano's sound and have no doubt that, had the piano been available, Bach would have chosen to write for it instead of the Harpsichord. I don't think any "spirit" is lost whatsoever on the piano - it's simply a superior instrument.
Then again, I've never been taken with the whole period instrument craze.