The most appropriate option to fill in the blank is eagerly.

The word "eagerly" means "with great interest or excitement". It is the most accurate word to describe a book that is anticipated by many people.

The other options are not as accurate.

• Deftly means "with skill and dexterity". It could be used to describe a book that is well-written, but it is not as specific as "eagerly".
• Badly means "in a poor or unsatisfactory way". It is not a positive word and it does not make sense to describe a book as "badly awaited".
• Slowly means "taking a long time to do something". It is not a positive word and it does not make sense to describe a book as "slowly awaited".