Business Unusual is a run of the mill 6th Doctor adventure which wouldn't seem out of place in series 24 had Colin Baker not been fired. The novel really is Doctor Who by numbers and you can imagine the story on screen in all it's naff glory. The biggest draw of this book is that it features the 6th Doctor meeting Mel "naturally" as in the TV show she was pulled out of time to testify in his trial, and also that the 6th Doctor finally gets a story with the Brigadier.
The trouble I found with Business Unusual is that it never seems to get out of 2nd gear. The novel chugs along nicely, but there is never any really exciting bits which make you want to keep reading. It does pick it up a bit from around the third mark, but still never really seems to hold your attention.
For those of you like me who were excited to see the introduction of Mel and the Doctor/Brig the book is a real let down. Mel was a real annoying character on screen (as was the 6th Doctor if we are honest) so I was hoping she would fare better in novel form, just like the 6th Doctor does, however she is equally as annoying, if not more so. She is rude to everyone, has a "holier than thou" attitude all the time and constantly bangs on about being healthy. As for the Doctor/Brig, they don't get much action together, and even then it's lacking, so it's a bit of a let down.
The enemy are a continuation of Gary Russell's novel "The Scales of Injustice" which is a nice twist given the business name, "SeneNet" and they are fairly interesting for the most part but the novel doesn't really do them justice.
In short Business Unusual is a little slow going, but other than that it's a perfectly enjoyable 6th Doctor adventure.