Long-winded and ever so surprisingly absorbing book (7)
I believe the answer is:
verbose
'long-winded' is the definition.
(long-winded can mean overly talkative or verbose)
'ever so surprisingly absorbing book' is the wordplay.
'surprisingly' indicates an anagram (a surprising ordering of the letters).
'absorbing' means one lot of letters goes inside another.
'book' becomes 'b' (abbreviation for book).
'ever'+'so'='everso'
'everso' with letters rearranged gives 'verose'.
'verose' enclosing 'b' is 'VERBOSE'.
'and' is the link.
(Other definitions for verbose that I've seen before include "Loquacious" , "Using too many words, too talkative" , "Observe (anag) -- long-winded" , "Boringly long-winded" , "Garrulous" .)