This book is really good, just a totally refreshing approach to playing and studying jazz. I think if you work from this, your improvisations will become more melodic and have more [i]meaning[/i]. Hal shows how the 'play this scale over that chord' approach to improvisation has its limitations - apparent when you look at what the masters [i]actually[/i] play on records.
some topics include
the importance of chord tone improvisation
RHYTHM!
how all 12 notes are available at any time
how to use substitutions over the original harmony (eg, superimposing triads)
Of course, it is still important to know your scales but Hal shows how to practice them so you get maximum benefit from them and you are making music, spelling out the changes in your lines without sounding like a beginner.
Highly recommended!