Complex sentence: The first BBC Books release was a novelisation of the television movie (considered a standalone work by some), but the run of "original" Eighth Doctor Adventures began in 1997 with "The Eight Doctors" by Terrance Dicks and continued until 2005.
Split into simpler sentences: The first BBC Books release was a novelisation of the television movie, but this was considered a standalone work. The Eighth Doctor Adventures series proper began in 1997 with "The Eight Doctors" by Terrance Dicks and continued until 2005.