Hislop's work, now over 100 years old, is still the best starting point for studying comparative religion. Of course, there is much in it that is no longer valid, and so long as the Vatican still stands,it will probably always feature on their banned books list (officially non-existent since 1966), however, the main points of the book are incontestable, which is probably why I know of no serious rebuttal.
Just a quick comment on those who feel such a book is an attack on their faith, true faith is not blind faith, and so if there was no dialogue on the foundations or basis of that faith, would it not prove to be built on sand? If genuine, not only would it withstand constuctive criticism, but would welcome it.