How does the change of shall
to the conjunctive form should
influence the issue? Well, as we will see the difference
is probably rather in style and in taste. I'd prefer
to say I recommend you read the book, or something similar.
Tthe main thing here is again Spanish and in Spanish
(at least in this aspect).
Este libro lo tienes
que leer. = This book you have to
read it. Este libro lo tendrías
que leer. = This book you would have
to read it. Este libro lo debes
leer.= This book you shall read it. Este libro lo deberías
leer.= This book you should read